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Honeywell Home evohome Stored Hot Water Kit ATF500DHW — CS92A BDR91 Cylinder Thermostat Wireless Zone Valve Control Vented Unvented
Honeywell Home evohome Stored Hot Water Kit ATF500DHW — CS92A BDR91 Cylinder Thermostat Wireless Zone Valve Control Vented Unvented
The Honeywell Home evohome Stored Hot Water Kit (ATF500DHW) is the dedicated accessory that adds full stored hot water control to any evohome system — enabling the evohome controller to manage, schedule, monitor, and remotely override the hot water cylinder alongside the heating zones it already controls. Compatible with both vented and unvented indirect cylinders. The kit contains a CS92A wireless battery-operated cylinder thermostat (with transceiver), a BDR91 wireless relay box to switch a 2-port zone valve or 3-port diverter valve, a T8674B strap-on sensor for vented cylinders, and a F420079510 insertion sensor for unvented cylinders. Once bound, the evohome controller displays the live hot water temperature on its main screen, allows schedule viewing and instant override, and hot water can be controlled remotely via the Total Connect Comfort app (iOS and Android). Battery life on the CS92A is typically at least 2 years on 2× AA alkaline cells. This kit is an add-on accessory — an existing evohome controller is required.
⚠ Requires an Existing evohome Controller — This kit does not include an evohome controller or touchscreen. It is an accessory that adds hot water control to an existing evohome installation. The evohome ATP921R2143 Thermostat Pack (or equivalent) must already be installed and operating. This kit cannot function as a standalone hot water controller.
ℹ Not for Combi Boilers — Stored Cylinder Systems Only
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
Vented & Unvented
Both cylinder types
CS92A + BDR91
Full wireless kit
App Control
Total Connect Comfort
2+ Years
Battery life (CS92A)
Features & Benefits
✔ CS92A Wireless Cylinder Thermostat — No Extra Wiring
The CS92A is a wireless, battery-operated cylinder thermostat that communicates with the evohome controller by radio — no additional wiring between the cylinder and the evohome system is needed. It mounts directly to the cylinder or pipework using the supplied sensor, and once bound to the evohome controller, it transmits live cylinder temperature readings to the controller screen. The CS92A is powered by 2× AA alkaline batteries with a typical life of at least 2 years, making it entirely independent of any cable run to the airing cupboard. This is a significant advantage over wired cylinder thermostats in properties where running a new cable from the cylinder to the programmer or wiring centre would be disruptive.
✔ BDR91 Wireless Relay Box — Zone Valve Control
The BDR91 wireless relay box receives switching commands from the evohome controller by radio and operates the hot water zone valve or diverter valve — the same way it switches heating zone valves in the rest of the evohome system. The relay box is wired to the zone valve's motor wires (the same connection a conventional programmer would use) and requires only a mains supply. For S-plan systems (separate zone valves for heating and hot water), the BDR91 switches the hot water zone valve independently. For Y-plan systems (a single 3-port diverter), the BDR91 provides the demand signal that calls for hot water via the diverter's mid-position.
✔ Both Vented & Unvented Sensors Included
The kit includes two temperature sensors for both cylinder types: the T8674B strap-on surface sensor is attached to the outside of the cylinder body and is used with vented (gravity-fed / open-vented) indirect cylinders where access to an immersion heater pocket is not available. The F420079510 insertion sensor inserts into the thermostat pocket on unvented (mains-pressure) cylinders for a more accurate in-cylinder temperature reading. Having both sensors in the box means the kit is compatible with virtually any stored cylinder installation without needing to order additional parts.
✔ Live Cylinder Temperature on the evohome Screen
Once bound, the evohome controller's main screen displays the actual live temperature of the stored hot water alongside the heating zone temperatures. This gives the homeowner a single dashboard showing the state of both heating and hot water from one location — no need to check a separate cylinder thermostat dial or programmer. The screen also shows the hot water schedule (the times when hot water heating is active) and allows the schedule to be overridden instantly with a single tap — boosting the hot water for an unexpected bath or guest without reprogramming the schedule.
✔ Remote Control via Total Connect Comfort App
Via the Honeywell Home Total Connect Comfort app (iOS and Android, free), the hot water can be monitored and controlled remotely from anywhere with an internet connection — the same app used to control the evohome heating zones. Check whether the hot water is on, boost it before returning home, cancel the afternoon cycle if plans change, or view the hot water temperature from the office. The evohome system also integrates with Amazon Alexa, Google Home, and Apple HomeKit for voice control via the wider evohome ecosystem.
✔ Time and Temperature Scheduling — LED Status Indicators
The hot water schedule is programmed on the evohome controller using the same interface as the heating zones — set the times and target temperatures for hot water heating across the day, with the system heating the cylinder to the set point temperature at the scheduled times and holding it there. The BDR91 relay box features clear LED status indicators showing whether the relay is energised (hot water called) or at rest, making commissioning checks and fault finding straightforward without needing to refer to the controller screen or app.
What's in the Box — ATF500DHW
| CS92A | Wireless battery-operated cylinder thermostat with transceiver — 2× AA alkaline (typical 2+ year life) |
| BDR91 | Wireless relay box — controls 2-port zone valve or 3-port diverter valve (mains wired) |
| T8674B | Strap-on surface sensor — for vented indirect cylinders |
| F420079510 | Insertion sensor — for unvented cylinders (inserts into thermostat pocket) |
| Documentation | Installation guide (including wiring diagrams for S-plan and Y-plan) |
Technical Specifications — ATF500DHW
| Manufacturer / MPN | Honeywell Home (by Resideo) — ATF500DHW |
| GTIN | 5025121382274 |
| Compatible System | Honeywell Home evohome (requires existing evohome controller) |
| Cylinder Compatibility | Vented (gravity-fed) indirect · Unvented (mains-pressure) indirect |
| Valve Compatibility | 2-port zone valve (S-plan) · 3-port diverter valve (Y-plan) |
| Communication | Wireless RF (evohome ecosystem protocol) |
| CS92A Power | 2× AA alkaline batteries — typical life 2+ years |
| BDR91 Power | 230V AC mains (wired to zone valve circuit) |
| App Control | Total Connect Comfort (iOS & Android) · Alexa · Google Home · Apple HomeKit |
| BDR91 LED Indicators | Yes — relay status, time and temperature set display |
| Weight (inc. packaging) | 0.662 kg |
| Warranty | 1 year — Honeywell Home manufacturer's warranty |
Frequently Asked Questions
Do I need this kit if I have a combi boiler?
No — combi boilers heat water on demand and have no stored cylinder to control. This kit is for properties with a system boiler or regular (heat-only) boiler that feeds an indirect hot water cylinder. If you have a combi boiler, the evohome system controls your central heating zones but there is nothing to add for hot water — it operates automatically whenever a hot tap is opened. Only purchase this kit if your property has a hot water cylinder in an airing cupboard or plant room.
Can I control the immersion heater with this kit?
The ATF500DHW controls the zone valve or diverter valve that routes boiler-heated water to the cylinder — it does not directly switch an immersion heater. The CS92A cylinder thermostat monitors temperature and signals the BDR91 relay, which in turn controls the valve. For direct immersion heater control, a separate dedicated immersion heater controller or timer would be needed. However, many properties use the immersion heater purely as a backup — if the cylinder is already zone-valve-controlled via the ATF500DHW, the immersion can be left on its standard thermostat as a safety fallback without requiring additional evohome integration.
What is the difference between S-plan and Y-plan, and does this kit work with both?
Yes — the ATF500DHW works with both. S-plan systems use separate 2-port motorised zone valves for the heating circuit and the hot water circuit — the BDR91 in this kit switches the hot water zone valve. Y-plan systems use a single 3-port mid-position diverter valve that routes flow to heating only, hot water only, or both simultaneously — the BDR91 provides the hot water demand signal to the diverter valve's mid-position terminal. The installation guide included in the box contains specific wiring diagrams for both S-plan and Y-plan configurations. If you are unsure which plan your system uses, an installer can identify it from the valve fitted to the pipework near the boiler.
Do I need to keep my existing programmer or wiring centre?
When the ATF500DHW is fully installed and controlling hot water via the BDR91, the hot water channels on an existing programmer are bypassed — the BDR91 takes over the switching function for the hot water zone valve. You can remove or bypass the programmer's hot water output, or leave the programmer in place with its hot water output permanently enabled (which passes control back to the BDR91 and CS92A). The evohome system and BDR91 become the new hot water controller. Your existing wiring centre (if fitted) typically remains in place as it provides the switching connections for the zone valves, pump, and boiler — the BDR91 replaces the demand signal input, not the wiring centre itself.
Where should I mount the CS92A and BDR91 — are there placement restrictions?
The CS92A cylinder thermostat should be mounted on the cylinder body or pipework adjacent to the cylinder, where it can receive the temperature signal from the selected sensor. Keep it away from direct heat sources and ensure it has clear RF line-of-sight (or minimal interference) to the evohome controller or a BDR91 used as a relay. The BDR91 should be mounted near the zone valve it controls, close to the wiring connections. Critically: do not mount the CS92A close to any BDR91 — the relay box generates RF interference that can disrupt the thermostat's transmission. Maintain at least 30cm separation between the CS92A and any BDR91 unit. Similarly, keep both units away from other RF sources, metal enclosures, and large electrical loads where possible.
$71.80
Original: $205.15
-65%Honeywell Home evohome Stored Hot Water Kit ATF500DHW — CS92A BDR91 Cylinder Thermostat Wireless Zone Valve Control Vented Unvented—
$205.15
$71.80Honeywell Home evohome Stored Hot Water Kit ATF500DHW — CS92A BDR91 Cylinder Thermostat Wireless Zone Valve Control Vented Unvented
The Honeywell Home evohome Stored Hot Water Kit (ATF500DHW) is the dedicated accessory that adds full stored hot water control to any evohome system — enabling the evohome controller to manage, schedule, monitor, and remotely override the hot water cylinder alongside the heating zones it already controls. Compatible with both vented and unvented indirect cylinders. The kit contains a CS92A wireless battery-operated cylinder thermostat (with transceiver), a BDR91 wireless relay box to switch a 2-port zone valve or 3-port diverter valve, a T8674B strap-on sensor for vented cylinders, and a F420079510 insertion sensor for unvented cylinders. Once bound, the evohome controller displays the live hot water temperature on its main screen, allows schedule viewing and instant override, and hot water can be controlled remotely via the Total Connect Comfort app (iOS and Android). Battery life on the CS92A is typically at least 2 years on 2× AA alkaline cells. This kit is an add-on accessory — an existing evohome controller is required.
⚠ Requires an Existing evohome Controller — This kit does not include an evohome controller or touchscreen. It is an accessory that adds hot water control to an existing evohome installation. The evohome ATP921R2143 Thermostat Pack (or equivalent) must already be installed and operating. This kit cannot function as a standalone hot water controller.
ℹ Not for Combi Boilers — Stored Cylinder Systems Only
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
Vented & Unvented
Both cylinder types
CS92A + BDR91
Full wireless kit
App Control
Total Connect Comfort
2+ Years
Battery life (CS92A)
Features & Benefits
✔ CS92A Wireless Cylinder Thermostat — No Extra Wiring
The CS92A is a wireless, battery-operated cylinder thermostat that communicates with the evohome controller by radio — no additional wiring between the cylinder and the evohome system is needed. It mounts directly to the cylinder or pipework using the supplied sensor, and once bound to the evohome controller, it transmits live cylinder temperature readings to the controller screen. The CS92A is powered by 2× AA alkaline batteries with a typical life of at least 2 years, making it entirely independent of any cable run to the airing cupboard. This is a significant advantage over wired cylinder thermostats in properties where running a new cable from the cylinder to the programmer or wiring centre would be disruptive.
✔ BDR91 Wireless Relay Box — Zone Valve Control
The BDR91 wireless relay box receives switching commands from the evohome controller by radio and operates the hot water zone valve or diverter valve — the same way it switches heating zone valves in the rest of the evohome system. The relay box is wired to the zone valve's motor wires (the same connection a conventional programmer would use) and requires only a mains supply. For S-plan systems (separate zone valves for heating and hot water), the BDR91 switches the hot water zone valve independently. For Y-plan systems (a single 3-port diverter), the BDR91 provides the demand signal that calls for hot water via the diverter's mid-position.
✔ Both Vented & Unvented Sensors Included
The kit includes two temperature sensors for both cylinder types: the T8674B strap-on surface sensor is attached to the outside of the cylinder body and is used with vented (gravity-fed / open-vented) indirect cylinders where access to an immersion heater pocket is not available. The F420079510 insertion sensor inserts into the thermostat pocket on unvented (mains-pressure) cylinders for a more accurate in-cylinder temperature reading. Having both sensors in the box means the kit is compatible with virtually any stored cylinder installation without needing to order additional parts.
✔ Live Cylinder Temperature on the evohome Screen
Once bound, the evohome controller's main screen displays the actual live temperature of the stored hot water alongside the heating zone temperatures. This gives the homeowner a single dashboard showing the state of both heating and hot water from one location — no need to check a separate cylinder thermostat dial or programmer. The screen also shows the hot water schedule (the times when hot water heating is active) and allows the schedule to be overridden instantly with a single tap — boosting the hot water for an unexpected bath or guest without reprogramming the schedule.
✔ Remote Control via Total Connect Comfort App
Via the Honeywell Home Total Connect Comfort app (iOS and Android, free), the hot water can be monitored and controlled remotely from anywhere with an internet connection — the same app used to control the evohome heating zones. Check whether the hot water is on, boost it before returning home, cancel the afternoon cycle if plans change, or view the hot water temperature from the office. The evohome system also integrates with Amazon Alexa, Google Home, and Apple HomeKit for voice control via the wider evohome ecosystem.
✔ Time and Temperature Scheduling — LED Status Indicators
The hot water schedule is programmed on the evohome controller using the same interface as the heating zones — set the times and target temperatures for hot water heating across the day, with the system heating the cylinder to the set point temperature at the scheduled times and holding it there. The BDR91 relay box features clear LED status indicators showing whether the relay is energised (hot water called) or at rest, making commissioning checks and fault finding straightforward without needing to refer to the controller screen or app.
What's in the Box — ATF500DHW
| CS92A | Wireless battery-operated cylinder thermostat with transceiver — 2× AA alkaline (typical 2+ year life) |
| BDR91 | Wireless relay box — controls 2-port zone valve or 3-port diverter valve (mains wired) |
| T8674B | Strap-on surface sensor — for vented indirect cylinders |
| F420079510 | Insertion sensor — for unvented cylinders (inserts into thermostat pocket) |
| Documentation | Installation guide (including wiring diagrams for S-plan and Y-plan) |
Technical Specifications — ATF500DHW
| Manufacturer / MPN | Honeywell Home (by Resideo) — ATF500DHW |
| GTIN | 5025121382274 |
| Compatible System | Honeywell Home evohome (requires existing evohome controller) |
| Cylinder Compatibility | Vented (gravity-fed) indirect · Unvented (mains-pressure) indirect |
| Valve Compatibility | 2-port zone valve (S-plan) · 3-port diverter valve (Y-plan) |
| Communication | Wireless RF (evohome ecosystem protocol) |
| CS92A Power | 2× AA alkaline batteries — typical life 2+ years |
| BDR91 Power | 230V AC mains (wired to zone valve circuit) |
| App Control | Total Connect Comfort (iOS & Android) · Alexa · Google Home · Apple HomeKit |
| BDR91 LED Indicators | Yes — relay status, time and temperature set display |
| Weight (inc. packaging) | 0.662 kg |
| Warranty | 1 year — Honeywell Home manufacturer's warranty |
Frequently Asked Questions
Do I need this kit if I have a combi boiler?
No — combi boilers heat water on demand and have no stored cylinder to control. This kit is for properties with a system boiler or regular (heat-only) boiler that feeds an indirect hot water cylinder. If you have a combi boiler, the evohome system controls your central heating zones but there is nothing to add for hot water — it operates automatically whenever a hot tap is opened. Only purchase this kit if your property has a hot water cylinder in an airing cupboard or plant room.
Can I control the immersion heater with this kit?
The ATF500DHW controls the zone valve or diverter valve that routes boiler-heated water to the cylinder — it does not directly switch an immersion heater. The CS92A cylinder thermostat monitors temperature and signals the BDR91 relay, which in turn controls the valve. For direct immersion heater control, a separate dedicated immersion heater controller or timer would be needed. However, many properties use the immersion heater purely as a backup — if the cylinder is already zone-valve-controlled via the ATF500DHW, the immersion can be left on its standard thermostat as a safety fallback without requiring additional evohome integration.
What is the difference between S-plan and Y-plan, and does this kit work with both?
Yes — the ATF500DHW works with both. S-plan systems use separate 2-port motorised zone valves for the heating circuit and the hot water circuit — the BDR91 in this kit switches the hot water zone valve. Y-plan systems use a single 3-port mid-position diverter valve that routes flow to heating only, hot water only, or both simultaneously — the BDR91 provides the hot water demand signal to the diverter valve's mid-position terminal. The installation guide included in the box contains specific wiring diagrams for both S-plan and Y-plan configurations. If you are unsure which plan your system uses, an installer can identify it from the valve fitted to the pipework near the boiler.
Do I need to keep my existing programmer or wiring centre?
When the ATF500DHW is fully installed and controlling hot water via the BDR91, the hot water channels on an existing programmer are bypassed — the BDR91 takes over the switching function for the hot water zone valve. You can remove or bypass the programmer's hot water output, or leave the programmer in place with its hot water output permanently enabled (which passes control back to the BDR91 and CS92A). The evohome system and BDR91 become the new hot water controller. Your existing wiring centre (if fitted) typically remains in place as it provides the switching connections for the zone valves, pump, and boiler — the BDR91 replaces the demand signal input, not the wiring centre itself.
Where should I mount the CS92A and BDR91 — are there placement restrictions?
The CS92A cylinder thermostat should be mounted on the cylinder body or pipework adjacent to the cylinder, where it can receive the temperature signal from the selected sensor. Keep it away from direct heat sources and ensure it has clear RF line-of-sight (or minimal interference) to the evohome controller or a BDR91 used as a relay. The BDR91 should be mounted near the zone valve it controls, close to the wiring connections. Critically: do not mount the CS92A close to any BDR91 — the relay box generates RF interference that can disrupt the thermostat's transmission. Maintain at least 30cm separation between the CS92A and any BDR91 unit. Similarly, keep both units away from other RF sources, metal enclosures, and large electrical loads where possible.
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
The Honeywell Home evohome Stored Hot Water Kit (ATF500DHW) is the dedicated accessory that adds full stored hot water control to any evohome system — enabling the evohome controller to manage, schedule, monitor, and remotely override the hot water cylinder alongside the heating zones it already controls. Compatible with both vented and unvented indirect cylinders. The kit contains a CS92A wireless battery-operated cylinder thermostat (with transceiver), a BDR91 wireless relay box to switch a 2-port zone valve or 3-port diverter valve, a T8674B strap-on sensor for vented cylinders, and a F420079510 insertion sensor for unvented cylinders. Once bound, the evohome controller displays the live hot water temperature on its main screen, allows schedule viewing and instant override, and hot water can be controlled remotely via the Total Connect Comfort app (iOS and Android). Battery life on the CS92A is typically at least 2 years on 2× AA alkaline cells. This kit is an add-on accessory — an existing evohome controller is required.
⚠ Requires an Existing evohome Controller — This kit does not include an evohome controller or touchscreen. It is an accessory that adds hot water control to an existing evohome installation. The evohome ATP921R2143 Thermostat Pack (or equivalent) must already be installed and operating. This kit cannot function as a standalone hot water controller.
ℹ Not for Combi Boilers — Stored Cylinder Systems Only
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
This kit controls stored hot water cylinders — it is designed for properties with a system boiler or heat-only (regular) boiler that heats an indirect hot water cylinder via a zone valve or diverter valve. It is not suitable for combi boilers, which produce hot water on demand without a storage cylinder. If you are unsure whether your system has a stored cylinder, check the airing cupboard — if there is an insulated hot water tank connected to the boiler via pipework, this kit applies. Combi boiler users do not need hot water control accessories.
Vented & Unvented
Both cylinder types
CS92A + BDR91
Full wireless kit
App Control
Total Connect Comfort
2+ Years
Battery life (CS92A)
Features & Benefits
✔ CS92A Wireless Cylinder Thermostat — No Extra Wiring
The CS92A is a wireless, battery-operated cylinder thermostat that communicates with the evohome controller by radio — no additional wiring between the cylinder and the evohome system is needed. It mounts directly to the cylinder or pipework using the supplied sensor, and once bound to the evohome controller, it transmits live cylinder temperature readings to the controller screen. The CS92A is powered by 2× AA alkaline batteries with a typical life of at least 2 years, making it entirely independent of any cable run to the airing cupboard. This is a significant advantage over wired cylinder thermostats in properties where running a new cable from the cylinder to the programmer or wiring centre would be disruptive.
✔ BDR91 Wireless Relay Box — Zone Valve Control
The BDR91 wireless relay box receives switching commands from the evohome controller by radio and operates the hot water zone valve or diverter valve — the same way it switches heating zone valves in the rest of the evohome system. The relay box is wired to the zone valve's motor wires (the same connection a conventional programmer would use) and requires only a mains supply. For S-plan systems (separate zone valves for heating and hot water), the BDR91 switches the hot water zone valve independently. For Y-plan systems (a single 3-port diverter), the BDR91 provides the demand signal that calls for hot water via the diverter's mid-position.
✔ Both Vented & Unvented Sensors Included
The kit includes two temperature sensors for both cylinder types: the T8674B strap-on surface sensor is attached to the outside of the cylinder body and is used with vented (gravity-fed / open-vented) indirect cylinders where access to an immersion heater pocket is not available. The F420079510 insertion sensor inserts into the thermostat pocket on unvented (mains-pressure) cylinders for a more accurate in-cylinder temperature reading. Having both sensors in the box means the kit is compatible with virtually any stored cylinder installation without needing to order additional parts.
✔ Live Cylinder Temperature on the evohome Screen
Once bound, the evohome controller's main screen displays the actual live temperature of the stored hot water alongside the heating zone temperatures. This gives the homeowner a single dashboard showing the state of both heating and hot water from one location — no need to check a separate cylinder thermostat dial or programmer. The screen also shows the hot water schedule (the times when hot water heating is active) and allows the schedule to be overridden instantly with a single tap — boosting the hot water for an unexpected bath or guest without reprogramming the schedule.
✔ Remote Control via Total Connect Comfort App
Via the Honeywell Home Total Connect Comfort app (iOS and Android, free), the hot water can be monitored and controlled remotely from anywhere with an internet connection — the same app used to control the evohome heating zones. Check whether the hot water is on, boost it before returning home, cancel the afternoon cycle if plans change, or view the hot water temperature from the office. The evohome system also integrates with Amazon Alexa, Google Home, and Apple HomeKit for voice control via the wider evohome ecosystem.
✔ Time and Temperature Scheduling — LED Status Indicators
The hot water schedule is programmed on the evohome controller using the same interface as the heating zones — set the times and target temperatures for hot water heating across the day, with the system heating the cylinder to the set point temperature at the scheduled times and holding it there. The BDR91 relay box features clear LED status indicators showing whether the relay is energised (hot water called) or at rest, making commissioning checks and fault finding straightforward without needing to refer to the controller screen or app.
What's in the Box — ATF500DHW
| CS92A | Wireless battery-operated cylinder thermostat with transceiver — 2× AA alkaline (typical 2+ year life) |
| BDR91 | Wireless relay box — controls 2-port zone valve or 3-port diverter valve (mains wired) |
| T8674B | Strap-on surface sensor — for vented indirect cylinders |
| F420079510 | Insertion sensor — for unvented cylinders (inserts into thermostat pocket) |
| Documentation | Installation guide (including wiring diagrams for S-plan and Y-plan) |
Technical Specifications — ATF500DHW
| Manufacturer / MPN | Honeywell Home (by Resideo) — ATF500DHW |
| GTIN | 5025121382274 |
| Compatible System | Honeywell Home evohome (requires existing evohome controller) |
| Cylinder Compatibility | Vented (gravity-fed) indirect · Unvented (mains-pressure) indirect |
| Valve Compatibility | 2-port zone valve (S-plan) · 3-port diverter valve (Y-plan) |
| Communication | Wireless RF (evohome ecosystem protocol) |
| CS92A Power | 2× AA alkaline batteries — typical life 2+ years |
| BDR91 Power | 230V AC mains (wired to zone valve circuit) |
| App Control | Total Connect Comfort (iOS & Android) · Alexa · Google Home · Apple HomeKit |
| BDR91 LED Indicators | Yes — relay status, time and temperature set display |
| Weight (inc. packaging) | 0.662 kg |
| Warranty | 1 year — Honeywell Home manufacturer's warranty |
Frequently Asked Questions
Do I need this kit if I have a combi boiler?
No — combi boilers heat water on demand and have no stored cylinder to control. This kit is for properties with a system boiler or regular (heat-only) boiler that feeds an indirect hot water cylinder. If you have a combi boiler, the evohome system controls your central heating zones but there is nothing to add for hot water — it operates automatically whenever a hot tap is opened. Only purchase this kit if your property has a hot water cylinder in an airing cupboard or plant room.
Can I control the immersion heater with this kit?
The ATF500DHW controls the zone valve or diverter valve that routes boiler-heated water to the cylinder — it does not directly switch an immersion heater. The CS92A cylinder thermostat monitors temperature and signals the BDR91 relay, which in turn controls the valve. For direct immersion heater control, a separate dedicated immersion heater controller or timer would be needed. However, many properties use the immersion heater purely as a backup — if the cylinder is already zone-valve-controlled via the ATF500DHW, the immersion can be left on its standard thermostat as a safety fallback without requiring additional evohome integration.
What is the difference between S-plan and Y-plan, and does this kit work with both?
Yes — the ATF500DHW works with both. S-plan systems use separate 2-port motorised zone valves for the heating circuit and the hot water circuit — the BDR91 in this kit switches the hot water zone valve. Y-plan systems use a single 3-port mid-position diverter valve that routes flow to heating only, hot water only, or both simultaneously — the BDR91 provides the hot water demand signal to the diverter valve's mid-position terminal. The installation guide included in the box contains specific wiring diagrams for both S-plan and Y-plan configurations. If you are unsure which plan your system uses, an installer can identify it from the valve fitted to the pipework near the boiler.
Do I need to keep my existing programmer or wiring centre?
When the ATF500DHW is fully installed and controlling hot water via the BDR91, the hot water channels on an existing programmer are bypassed — the BDR91 takes over the switching function for the hot water zone valve. You can remove or bypass the programmer's hot water output, or leave the programmer in place with its hot water output permanently enabled (which passes control back to the BDR91 and CS92A). The evohome system and BDR91 become the new hot water controller. Your existing wiring centre (if fitted) typically remains in place as it provides the switching connections for the zone valves, pump, and boiler — the BDR91 replaces the demand signal input, not the wiring centre itself.
Where should I mount the CS92A and BDR91 — are there placement restrictions?
The CS92A cylinder thermostat should be mounted on the cylinder body or pipework adjacent to the cylinder, where it can receive the temperature signal from the selected sensor. Keep it away from direct heat sources and ensure it has clear RF line-of-sight (or minimal interference) to the evohome controller or a BDR91 used as a relay. The BDR91 should be mounted near the zone valve it controls, close to the wiring connections. Critically: do not mount the CS92A close to any BDR91 — the relay box generates RF interference that can disrupt the thermostat's transmission. Maintain at least 30cm separation between the CS92A and any BDR91 unit. Similarly, keep both units away from other RF sources, metal enclosures, and large electrical loads where possible.
