✨ New Arrivals Just Dropped!Explore
OSO Super Xpress S2X 300L Direct Unvented Hot Water Cylinder | Pre-Plumbed Electric
Direct Unvented CylinderS2X 300LPre-Plumbed & Pre-Wired30% More Hot WaterTwin 3+3 kW Immersion25-Year Cylinder WarrantyOff-Peak Tariff Ready
The OSO Super Xpress 2.0 (S2X) 300L is a direct electric unvented hot water cylinder that delivers up to 30% more usable hot water than comparable competitor cylinders, thanks to OSO's unique temperature stratification and cylinder geometry optimisation. Using OSO's patented S-DESIGN, all pipework, expansion vessels, and electrical cables are concealed under a lid for a clean, professional finish. The S2X 300L is insulated with 4th-generation PUR foam for excellent heat retention and low standing losses. Twin 3 kW TITANIUM IMMERSION heaters (upper and lower) provide both rapid heat-up and off-peak economy flexibility. The entire G3 Building Regulations kit — expansion vessels, inlet control valve, tundish, drain cock — is factory-fitted, saving significant installation time. The S2X is built from stainless steel using OSO's ULTRAWELD Duplex laser-welded construction and backed by a 25-year cylinder warranty.
Key Features
- Up to 30% MORE usable hot water than competitor cylinders of the same nominal volume
- Effective hot water capacity at 40°C: 495L from a 300L cylinder
- S-DESIGN: all pipe connections exit from the rear, all concealed under lid — clean professional finish
- 4th-generation PUR foam insulation for reduced standing heat loss
- Twin 3+3 kW TITANIUM IMMERSION heaters — upper element for rapid heat-up, lower for off-peak economy heating
- TARIFF-READY: twin immersion configuration supports off-peak (Economy 7 / Economy 10) tariffs
- 75°C thermostat setpoint — maximises stratification and effective hot water availability
- Fully pre-plumbed and wired — integral expansion vessels and valve set factory-fitted, saving up to 70% installation time
- Integral G3 kit: 2 × 8L expansion vessels, strainer, PRV, expansion relief, drain cock, tundish — all factory-fitted
- Mixing valve preset to 60°C — scalding protection at draw-off points
- Mains pressure hot water delivery to all outlets — no need for a pump
- ULTRAWELD Duplex stainless steel laser-welded construction — 25-year cylinder warranty
- NANOPUR high-grade insulation system
- Shortest cylinder system on the market — enables downsizing to a smaller volume with the same hot water output
- XL tapping profile — suitable for large family homes and high-demand properties
OSO Technology Advantages
S-DESIGN — All Connections HiddenNANOPUR — High-Grade InsulationULTRAWELD — Superior Corrosion ResistanceTITANIUM IMMERSION — Hard Water DurabilityTARIFF-READY — Twin Immersions
What's Included
S2X 300L direct cylinder (pre-plumbed & pre-wired)
Twin 3+3 kW TITANIUM IMMERSION heaters (factory-fitted)
Mixing valve — preset 60°C
P&T safety valve (10 bar / 90–95°C)
2 × 8L integral expansion vessels (factory-fitted)
Inlet control valve (strainer + PRV + expansion relief)
Drain cock
Tundish
Fitting template
Installation manual
Technical Specifications
| Specification | Unit | Value |
|---|---|---|
| Product Number | OSO | 11011690 |
| Product Name | S2X 300 | |
| Nominal Volume | L | 280 |
| Effective Capacity at 40°C | L | 495 |
| Dimensions (H × Ø) | mm | 1780 × 595 |
| Weight (empty) | kg | 56 |
| Weight (full) | kg | 336 |
| Thermostat Setpoint | °C | 75 |
| Heat Loss (EN 12897) | W | 82 |
| Heat Loss / 24 hrs | kWh/day | 1.968 |
| Annual Energy Consumption | kWh/year | 4478 |
| Energy Efficiency | % | 37.4 |
| Energy Rating | D | |
| Tapping Profile | XL | |
| Immersion Power | 3+3 kW | |
| Electrical Supply | V | 240 V single-phase |
| Max Operating Pressure | bar | 6 |
| Expansion Vessels | 2 × 8L factory-fitted | |
| Mixing Valve Preset | °C | 60 |
| P&T Valve Rating | 10 bar / 90–95°C | |
| Cylinder Material | Stainless steel — ULTRAWELD Duplex laser-welded | |
| Immersion Type | TITANIUM IMMERSION (upper + lower) | |
| Insulation | 4th-generation PUR foam (NANOPUR) | |
| Cylinder Warranty | 25 years |
ℹ️ Downsize with confidence: Because the S2X 300L delivers up to 30% more usable hot water than competitor cylinders of the same nominal size, many installers can specify a smaller S2X model and achieve the same or better hot water delivery. A smaller cylinder also means lower standing heat losses, helping with SAP / Part L compliance.
Installation Overview
⚠️ G3-qualified installer required: Installation must be carried out by an installer holding a current G3 Unvented Hot Water Systems qualification. All electrical work must comply with BS 7671. Notify Building Control if required by local authority.
- Check dimensions and floor load: Confirm the cylinder footprint (1780mm H × 595mm Ø) fits the installation space. Allow a minimum 150mm clearance at the rear for connections and 400mm above the unit. Verify the floor can support the loaded weight (336 kg).
- Fix the fitting template: Tape the supplied template to the rear wall. Mark and drill the positions for the rear pipe tails. The S-DESIGN has all connections exiting from the rear — connect the pre-cut pipe tails to your distribution pipework before sliding the cylinder into place.
- Cold water supply: Connect the mains cold supply to the integrated inlet control valve. Ensure mains pressure is within the 6-bar working pressure limit — fit an upstream PRV if needed. Do not use the balanced cold outlet for anything other than mixer showers (Water Regulations).
- Hot water and distribution pipework: Connect the hot water outlet to your distribution pipework. The factory-set 60°C mixing valve provides scalding protection. The S2X delivers mains pressure hot water — no pump is required.
- Tundish and discharge pipe: Connect the tundish discharge to a suitable indirect discharge pipe with the correct air gap, positioned in accordance with BS 6700 and Building Regulations Part G.
- Electrical connections: Connect each immersion heater element to its own dedicated 240V 13A FCU. The lower element is typically wired to an off-peak tariff supply (Economy 7 / Economy 10) and the upper to the standard supply for top-up heating. Follow the wiring diagram in the installation manual.
- Fill, commission and test: Fill slowly with cold water. Bleed air from all hot outlets. Check for leaks. Switch on and allow to reach operating temperature. Test the mixing valve outlet temperature. Complete the G3 commissioning record.
Frequently Asked Questions
How does the S2X deliver 30% more hot water than other cylinders?
The S2X achieves this through a combination of precise cylinder geometry, temperature stratification at 75°C, and OSO's unique design. At 75°C, the stored water volume contains significantly more heat energy than competitors' cylinders set at 60°C. The effective usable capacity at 40°C draw-off temperature is 495L — well above the nominal 300L. This means you can often downsize, saving cost, space, and standing heat losses.
What is the difference between the upper and lower immersion heaters?
The S2X has twin 3 kW immersion heaters. The upper element heats only the top portion of the cylinder for quick heat recovery — useful when you've used some hot water and need a rapid top-up. The lower element heats the full cylinder volume and is typically connected to an off-peak tariff (Economy 7 or Economy 10) to heat the whole tank overnight at cheaper rates. Both work independently.
Is the S2X suitable for off-peak electricity tariffs?
Yes — the twin immersion design is specifically described as TARIFF-READY. The lower immersion can be wired to an off-peak supply and the upper to a standard supply. During off-peak hours, the lower element heats the full cylinder; during the day, the upper element provides top-up heating at any time. This can significantly reduce running costs.
Can I install an S2X 300L as a replacement for an existing vented cylinder?
Yes, but you'll need to ensure your water supply is mains-fed (i.e. adequate mains pressure) and that there is no gravity-fed storage tank supplying the current system. A G3-qualified installer must carry out the installation, and Building Control notification may be required. The S-DESIGN rear-connection system also means the cylinder must have rear wall clearance of at least 150mm.
What warranty does the S2X carry?
The stainless steel cylinder carries a 25-year warranty against defects in materials and manufacture — one of the best warranties in the UK market. Electrical components and valve gear carry a 2-year warranty.
Is the S2X hard water compatible?
Yes. TITANIUM IMMERSION heaters are used throughout the S2X range, providing superior durability in hard water areas compared to standard stainless steel or incoloy elements. The Duplex stainless steel cylinder body is also inherently scale-resistant.
Does the S2X need a pump to deliver mains pressure hot water?
No. The S2X is an unvented cylinder connected directly to the mains cold water supply. Hot water is delivered at mains pressure to all outlets — no pump or header tank is required. This makes it ideal for power showers and multi-outlet simultaneous use.
What is the tapping profile and what does XL mean?
The tapping profile is an ErP (Energy-related Products) classification describing how much hot water the cylinder can deliver in a standardised draw-off test. XL is a high-output profile, confirming the S2X is suitable for large households with multiple simultaneous outlets or high hot water demand.
Is G3 compliance documentation included with the cylinder?
Yes — the factory-fitted G3 kit (expansion vessels, PRV, strainer, expansion relief, tundish, drain cock) means all the compliance components are already installed. Your G3-qualified installer will complete the commissioning checklist, which forms the compliance record for Building Regulations Part G3.
Can the S2X be installed in an airing cupboard?
Yes. The S2X 300L requires 1780mm height clearance and 595mm diameter, plus 150mm rear clearance. The S-DESIGN concealed pipework keeps the installation tidy.
$728.42
Original: $2,081.19
-65%OSO Super Xpress S2X 300L Direct Unvented Hot Water Cylinder | Pre-Plumbed Electric—
$2,081.19
$728.42More Images
OSO Super Xpress S2X 300L Direct Unvented Hot Water Cylinder | Pre-Plumbed Electric
Direct Unvented CylinderS2X 300LPre-Plumbed & Pre-Wired30% More Hot WaterTwin 3+3 kW Immersion25-Year Cylinder WarrantyOff-Peak Tariff Ready
The OSO Super Xpress 2.0 (S2X) 300L is a direct electric unvented hot water cylinder that delivers up to 30% more usable hot water than comparable competitor cylinders, thanks to OSO's unique temperature stratification and cylinder geometry optimisation. Using OSO's patented S-DESIGN, all pipework, expansion vessels, and electrical cables are concealed under a lid for a clean, professional finish. The S2X 300L is insulated with 4th-generation PUR foam for excellent heat retention and low standing losses. Twin 3 kW TITANIUM IMMERSION heaters (upper and lower) provide both rapid heat-up and off-peak economy flexibility. The entire G3 Building Regulations kit — expansion vessels, inlet control valve, tundish, drain cock — is factory-fitted, saving significant installation time. The S2X is built from stainless steel using OSO's ULTRAWELD Duplex laser-welded construction and backed by a 25-year cylinder warranty.
Key Features
- Up to 30% MORE usable hot water than competitor cylinders of the same nominal volume
- Effective hot water capacity at 40°C: 495L from a 300L cylinder
- S-DESIGN: all pipe connections exit from the rear, all concealed under lid — clean professional finish
- 4th-generation PUR foam insulation for reduced standing heat loss
- Twin 3+3 kW TITANIUM IMMERSION heaters — upper element for rapid heat-up, lower for off-peak economy heating
- TARIFF-READY: twin immersion configuration supports off-peak (Economy 7 / Economy 10) tariffs
- 75°C thermostat setpoint — maximises stratification and effective hot water availability
- Fully pre-plumbed and wired — integral expansion vessels and valve set factory-fitted, saving up to 70% installation time
- Integral G3 kit: 2 × 8L expansion vessels, strainer, PRV, expansion relief, drain cock, tundish — all factory-fitted
- Mixing valve preset to 60°C — scalding protection at draw-off points
- Mains pressure hot water delivery to all outlets — no need for a pump
- ULTRAWELD Duplex stainless steel laser-welded construction — 25-year cylinder warranty
- NANOPUR high-grade insulation system
- Shortest cylinder system on the market — enables downsizing to a smaller volume with the same hot water output
- XL tapping profile — suitable for large family homes and high-demand properties
OSO Technology Advantages
S-DESIGN — All Connections HiddenNANOPUR — High-Grade InsulationULTRAWELD — Superior Corrosion ResistanceTITANIUM IMMERSION — Hard Water DurabilityTARIFF-READY — Twin Immersions
What's Included
S2X 300L direct cylinder (pre-plumbed & pre-wired)
Twin 3+3 kW TITANIUM IMMERSION heaters (factory-fitted)
Mixing valve — preset 60°C
P&T safety valve (10 bar / 90–95°C)
2 × 8L integral expansion vessels (factory-fitted)
Inlet control valve (strainer + PRV + expansion relief)
Drain cock
Tundish
Fitting template
Installation manual
Technical Specifications
| Specification | Unit | Value |
|---|---|---|
| Product Number | OSO | 11011690 |
| Product Name | S2X 300 | |
| Nominal Volume | L | 280 |
| Effective Capacity at 40°C | L | 495 |
| Dimensions (H × Ø) | mm | 1780 × 595 |
| Weight (empty) | kg | 56 |
| Weight (full) | kg | 336 |
| Thermostat Setpoint | °C | 75 |
| Heat Loss (EN 12897) | W | 82 |
| Heat Loss / 24 hrs | kWh/day | 1.968 |
| Annual Energy Consumption | kWh/year | 4478 |
| Energy Efficiency | % | 37.4 |
| Energy Rating | D | |
| Tapping Profile | XL | |
| Immersion Power | 3+3 kW | |
| Electrical Supply | V | 240 V single-phase |
| Max Operating Pressure | bar | 6 |
| Expansion Vessels | 2 × 8L factory-fitted | |
| Mixing Valve Preset | °C | 60 |
| P&T Valve Rating | 10 bar / 90–95°C | |
| Cylinder Material | Stainless steel — ULTRAWELD Duplex laser-welded | |
| Immersion Type | TITANIUM IMMERSION (upper + lower) | |
| Insulation | 4th-generation PUR foam (NANOPUR) | |
| Cylinder Warranty | 25 years |
ℹ️ Downsize with confidence: Because the S2X 300L delivers up to 30% more usable hot water than competitor cylinders of the same nominal size, many installers can specify a smaller S2X model and achieve the same or better hot water delivery. A smaller cylinder also means lower standing heat losses, helping with SAP / Part L compliance.
Installation Overview
⚠️ G3-qualified installer required: Installation must be carried out by an installer holding a current G3 Unvented Hot Water Systems qualification. All electrical work must comply with BS 7671. Notify Building Control if required by local authority.
- Check dimensions and floor load: Confirm the cylinder footprint (1780mm H × 595mm Ø) fits the installation space. Allow a minimum 150mm clearance at the rear for connections and 400mm above the unit. Verify the floor can support the loaded weight (336 kg).
- Fix the fitting template: Tape the supplied template to the rear wall. Mark and drill the positions for the rear pipe tails. The S-DESIGN has all connections exiting from the rear — connect the pre-cut pipe tails to your distribution pipework before sliding the cylinder into place.
- Cold water supply: Connect the mains cold supply to the integrated inlet control valve. Ensure mains pressure is within the 6-bar working pressure limit — fit an upstream PRV if needed. Do not use the balanced cold outlet for anything other than mixer showers (Water Regulations).
- Hot water and distribution pipework: Connect the hot water outlet to your distribution pipework. The factory-set 60°C mixing valve provides scalding protection. The S2X delivers mains pressure hot water — no pump is required.
- Tundish and discharge pipe: Connect the tundish discharge to a suitable indirect discharge pipe with the correct air gap, positioned in accordance with BS 6700 and Building Regulations Part G.
- Electrical connections: Connect each immersion heater element to its own dedicated 240V 13A FCU. The lower element is typically wired to an off-peak tariff supply (Economy 7 / Economy 10) and the upper to the standard supply for top-up heating. Follow the wiring diagram in the installation manual.
- Fill, commission and test: Fill slowly with cold water. Bleed air from all hot outlets. Check for leaks. Switch on and allow to reach operating temperature. Test the mixing valve outlet temperature. Complete the G3 commissioning record.
Frequently Asked Questions
How does the S2X deliver 30% more hot water than other cylinders?
The S2X achieves this through a combination of precise cylinder geometry, temperature stratification at 75°C, and OSO's unique design. At 75°C, the stored water volume contains significantly more heat energy than competitors' cylinders set at 60°C. The effective usable capacity at 40°C draw-off temperature is 495L — well above the nominal 300L. This means you can often downsize, saving cost, space, and standing heat losses.
What is the difference between the upper and lower immersion heaters?
The S2X has twin 3 kW immersion heaters. The upper element heats only the top portion of the cylinder for quick heat recovery — useful when you've used some hot water and need a rapid top-up. The lower element heats the full cylinder volume and is typically connected to an off-peak tariff (Economy 7 or Economy 10) to heat the whole tank overnight at cheaper rates. Both work independently.
Is the S2X suitable for off-peak electricity tariffs?
Yes — the twin immersion design is specifically described as TARIFF-READY. The lower immersion can be wired to an off-peak supply and the upper to a standard supply. During off-peak hours, the lower element heats the full cylinder; during the day, the upper element provides top-up heating at any time. This can significantly reduce running costs.
Can I install an S2X 300L as a replacement for an existing vented cylinder?
Yes, but you'll need to ensure your water supply is mains-fed (i.e. adequate mains pressure) and that there is no gravity-fed storage tank supplying the current system. A G3-qualified installer must carry out the installation, and Building Control notification may be required. The S-DESIGN rear-connection system also means the cylinder must have rear wall clearance of at least 150mm.
What warranty does the S2X carry?
The stainless steel cylinder carries a 25-year warranty against defects in materials and manufacture — one of the best warranties in the UK market. Electrical components and valve gear carry a 2-year warranty.
Is the S2X hard water compatible?
Yes. TITANIUM IMMERSION heaters are used throughout the S2X range, providing superior durability in hard water areas compared to standard stainless steel or incoloy elements. The Duplex stainless steel cylinder body is also inherently scale-resistant.
Does the S2X need a pump to deliver mains pressure hot water?
No. The S2X is an unvented cylinder connected directly to the mains cold water supply. Hot water is delivered at mains pressure to all outlets — no pump or header tank is required. This makes it ideal for power showers and multi-outlet simultaneous use.
What is the tapping profile and what does XL mean?
The tapping profile is an ErP (Energy-related Products) classification describing how much hot water the cylinder can deliver in a standardised draw-off test. XL is a high-output profile, confirming the S2X is suitable for large households with multiple simultaneous outlets or high hot water demand.
Is G3 compliance documentation included with the cylinder?
Yes — the factory-fitted G3 kit (expansion vessels, PRV, strainer, expansion relief, tundish, drain cock) means all the compliance components are already installed. Your G3-qualified installer will complete the commissioning checklist, which forms the compliance record for Building Regulations Part G3.
Can the S2X be installed in an airing cupboard?
Yes. The S2X 300L requires 1780mm height clearance and 595mm diameter, plus 150mm rear clearance. The S-DESIGN concealed pipework keeps the installation tidy.
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
Direct Unvented CylinderS2X 300LPre-Plumbed & Pre-Wired30% More Hot WaterTwin 3+3 kW Immersion25-Year Cylinder WarrantyOff-Peak Tariff Ready
The OSO Super Xpress 2.0 (S2X) 300L is a direct electric unvented hot water cylinder that delivers up to 30% more usable hot water than comparable competitor cylinders, thanks to OSO's unique temperature stratification and cylinder geometry optimisation. Using OSO's patented S-DESIGN, all pipework, expansion vessels, and electrical cables are concealed under a lid for a clean, professional finish. The S2X 300L is insulated with 4th-generation PUR foam for excellent heat retention and low standing losses. Twin 3 kW TITANIUM IMMERSION heaters (upper and lower) provide both rapid heat-up and off-peak economy flexibility. The entire G3 Building Regulations kit — expansion vessels, inlet control valve, tundish, drain cock — is factory-fitted, saving significant installation time. The S2X is built from stainless steel using OSO's ULTRAWELD Duplex laser-welded construction and backed by a 25-year cylinder warranty.
Key Features
- Up to 30% MORE usable hot water than competitor cylinders of the same nominal volume
- Effective hot water capacity at 40°C: 495L from a 300L cylinder
- S-DESIGN: all pipe connections exit from the rear, all concealed under lid — clean professional finish
- 4th-generation PUR foam insulation for reduced standing heat loss
- Twin 3+3 kW TITANIUM IMMERSION heaters — upper element for rapid heat-up, lower for off-peak economy heating
- TARIFF-READY: twin immersion configuration supports off-peak (Economy 7 / Economy 10) tariffs
- 75°C thermostat setpoint — maximises stratification and effective hot water availability
- Fully pre-plumbed and wired — integral expansion vessels and valve set factory-fitted, saving up to 70% installation time
- Integral G3 kit: 2 × 8L expansion vessels, strainer, PRV, expansion relief, drain cock, tundish — all factory-fitted
- Mixing valve preset to 60°C — scalding protection at draw-off points
- Mains pressure hot water delivery to all outlets — no need for a pump
- ULTRAWELD Duplex stainless steel laser-welded construction — 25-year cylinder warranty
- NANOPUR high-grade insulation system
- Shortest cylinder system on the market — enables downsizing to a smaller volume with the same hot water output
- XL tapping profile — suitable for large family homes and high-demand properties
OSO Technology Advantages
S-DESIGN — All Connections HiddenNANOPUR — High-Grade InsulationULTRAWELD — Superior Corrosion ResistanceTITANIUM IMMERSION — Hard Water DurabilityTARIFF-READY — Twin Immersions
What's Included
S2X 300L direct cylinder (pre-plumbed & pre-wired)
Twin 3+3 kW TITANIUM IMMERSION heaters (factory-fitted)
Mixing valve — preset 60°C
P&T safety valve (10 bar / 90–95°C)
2 × 8L integral expansion vessels (factory-fitted)
Inlet control valve (strainer + PRV + expansion relief)
Drain cock
Tundish
Fitting template
Installation manual
Technical Specifications
| Specification | Unit | Value |
|---|---|---|
| Product Number | OSO | 11011690 |
| Product Name | S2X 300 | |
| Nominal Volume | L | 280 |
| Effective Capacity at 40°C | L | 495 |
| Dimensions (H × Ø) | mm | 1780 × 595 |
| Weight (empty) | kg | 56 |
| Weight (full) | kg | 336 |
| Thermostat Setpoint | °C | 75 |
| Heat Loss (EN 12897) | W | 82 |
| Heat Loss / 24 hrs | kWh/day | 1.968 |
| Annual Energy Consumption | kWh/year | 4478 |
| Energy Efficiency | % | 37.4 |
| Energy Rating | D | |
| Tapping Profile | XL | |
| Immersion Power | 3+3 kW | |
| Electrical Supply | V | 240 V single-phase |
| Max Operating Pressure | bar | 6 |
| Expansion Vessels | 2 × 8L factory-fitted | |
| Mixing Valve Preset | °C | 60 |
| P&T Valve Rating | 10 bar / 90–95°C | |
| Cylinder Material | Stainless steel — ULTRAWELD Duplex laser-welded | |
| Immersion Type | TITANIUM IMMERSION (upper + lower) | |
| Insulation | 4th-generation PUR foam (NANOPUR) | |
| Cylinder Warranty | 25 years |
ℹ️ Downsize with confidence: Because the S2X 300L delivers up to 30% more usable hot water than competitor cylinders of the same nominal size, many installers can specify a smaller S2X model and achieve the same or better hot water delivery. A smaller cylinder also means lower standing heat losses, helping with SAP / Part L compliance.
Installation Overview
⚠️ G3-qualified installer required: Installation must be carried out by an installer holding a current G3 Unvented Hot Water Systems qualification. All electrical work must comply with BS 7671. Notify Building Control if required by local authority.
- Check dimensions and floor load: Confirm the cylinder footprint (1780mm H × 595mm Ø) fits the installation space. Allow a minimum 150mm clearance at the rear for connections and 400mm above the unit. Verify the floor can support the loaded weight (336 kg).
- Fix the fitting template: Tape the supplied template to the rear wall. Mark and drill the positions for the rear pipe tails. The S-DESIGN has all connections exiting from the rear — connect the pre-cut pipe tails to your distribution pipework before sliding the cylinder into place.
- Cold water supply: Connect the mains cold supply to the integrated inlet control valve. Ensure mains pressure is within the 6-bar working pressure limit — fit an upstream PRV if needed. Do not use the balanced cold outlet for anything other than mixer showers (Water Regulations).
- Hot water and distribution pipework: Connect the hot water outlet to your distribution pipework. The factory-set 60°C mixing valve provides scalding protection. The S2X delivers mains pressure hot water — no pump is required.
- Tundish and discharge pipe: Connect the tundish discharge to a suitable indirect discharge pipe with the correct air gap, positioned in accordance with BS 6700 and Building Regulations Part G.
- Electrical connections: Connect each immersion heater element to its own dedicated 240V 13A FCU. The lower element is typically wired to an off-peak tariff supply (Economy 7 / Economy 10) and the upper to the standard supply for top-up heating. Follow the wiring diagram in the installation manual.
- Fill, commission and test: Fill slowly with cold water. Bleed air from all hot outlets. Check for leaks. Switch on and allow to reach operating temperature. Test the mixing valve outlet temperature. Complete the G3 commissioning record.
Frequently Asked Questions
How does the S2X deliver 30% more hot water than other cylinders?
The S2X achieves this through a combination of precise cylinder geometry, temperature stratification at 75°C, and OSO's unique design. At 75°C, the stored water volume contains significantly more heat energy than competitors' cylinders set at 60°C. The effective usable capacity at 40°C draw-off temperature is 495L — well above the nominal 300L. This means you can often downsize, saving cost, space, and standing heat losses.
What is the difference between the upper and lower immersion heaters?
The S2X has twin 3 kW immersion heaters. The upper element heats only the top portion of the cylinder for quick heat recovery — useful when you've used some hot water and need a rapid top-up. The lower element heats the full cylinder volume and is typically connected to an off-peak tariff (Economy 7 or Economy 10) to heat the whole tank overnight at cheaper rates. Both work independently.
Is the S2X suitable for off-peak electricity tariffs?
Yes — the twin immersion design is specifically described as TARIFF-READY. The lower immersion can be wired to an off-peak supply and the upper to a standard supply. During off-peak hours, the lower element heats the full cylinder; during the day, the upper element provides top-up heating at any time. This can significantly reduce running costs.
Can I install an S2X 300L as a replacement for an existing vented cylinder?
Yes, but you'll need to ensure your water supply is mains-fed (i.e. adequate mains pressure) and that there is no gravity-fed storage tank supplying the current system. A G3-qualified installer must carry out the installation, and Building Control notification may be required. The S-DESIGN rear-connection system also means the cylinder must have rear wall clearance of at least 150mm.
What warranty does the S2X carry?
The stainless steel cylinder carries a 25-year warranty against defects in materials and manufacture — one of the best warranties in the UK market. Electrical components and valve gear carry a 2-year warranty.
Is the S2X hard water compatible?
Yes. TITANIUM IMMERSION heaters are used throughout the S2X range, providing superior durability in hard water areas compared to standard stainless steel or incoloy elements. The Duplex stainless steel cylinder body is also inherently scale-resistant.
Does the S2X need a pump to deliver mains pressure hot water?
No. The S2X is an unvented cylinder connected directly to the mains cold water supply. Hot water is delivered at mains pressure to all outlets — no pump or header tank is required. This makes it ideal for power showers and multi-outlet simultaneous use.
What is the tapping profile and what does XL mean?
The tapping profile is an ErP (Energy-related Products) classification describing how much hot water the cylinder can deliver in a standardised draw-off test. XL is a high-output profile, confirming the S2X is suitable for large households with multiple simultaneous outlets or high hot water demand.
Is G3 compliance documentation included with the cylinder?
Yes — the factory-fitted G3 kit (expansion vessels, PRV, strainer, expansion relief, tundish, drain cock) means all the compliance components are already installed. Your G3-qualified installer will complete the commissioning checklist, which forms the compliance record for Building Regulations Part G3.
Can the S2X be installed in an airing cupboard?
Yes. The S2X 300L requires 1780mm height clearance and 595mm diameter, plus 150mm rear clearance. The S-DESIGN concealed pipework keeps the installation tidy.
