The UFH Mixing Valve / Pump Set with Wilo Para 25/6-43/SCU is a complete, installer-ready solution for controlling water temperature in wet underfloor heating systems. Comprising a 1" thermostatic blending valve, the market-leading Wilo Para 25/6-43/SCU 'A'-rated circulating pump, and an integrated temperature controller with sensor, it delivers precise, stable supply temperatures to your UFH manifold. Suitable for systems up to 250 m² or 20 kW output, the unit is engineered for manifold installation with a lightweight, wall-mountable design and a dedicated air-vent port. Also available separately: the Honeywell V4043H motorised 2-port zone valve (22 mm or 28 mm) — the UK installer standard for zone-level flow control.

250 m²

Max floor area

20 kW

Max heat output

35–60 °C

Temp control range

±1 °C

Temp accuracy

EEI ≤0.21

Wilo pump rating

6 m

Max pump head

Installation Requirement: This pump set must be installed by a suitably qualified heating engineer. All electrical connections must comply with current IEE Wiring Regulations. Ensure a fused isolator with minimum 3 mm contact separation is fitted before the zone valve.

Compatibility Note: The mixing unit uses a 1" (G 1½") connection — verify manifold port sizing before ordering. The Honeywell V4043H valve must not be mounted with the powerhead below the horizontal level of the pipework, and must not block any vent or cold feed when in the closed position.

Complete UFH Control Solution: Together, the mixing unit and Honeywell zone valve provide precise temperature blending at the manifold and on/off zone control at the circuit level — the two fundamental layers of control needed for a properly designed wet UFH system.

Mixing Valve / Pump Set — Key Features

Wilo Para 25/6-43/SCU — 'A'-Rated Pump

The Wilo Para 25/6-43/SCU is a high-efficiency, glandless Class A circulator with an integrated differential pressure control and Green Button self-controlled technology that automatically adjusts pump speed to match system demand — no external controller needed. It delivers 3× higher starting torque than comparable heating pumps, making it exceptionally reliable in systems with residual scale or after periods of inactivity. The 130 mm port-to-port length and G 1½" connections fit the mixing unit directly.

Thermostatic Blending Valve

A precision brass (HPB57-3) 1" blending valve with a manual mixing core and thermosensitive element regulates the hot/cold ratio, delivering a stable supply temperature to ±1 °C across the full 35–60 °C operating range. Rated to 10 bar and 100 °C, it is compatible with all standard boilers and heat pumps and sized to support systems up to 250 m² / 20 kW.

Integrated Temperature Controller & Sensor

The built-in temperature controller and dedicated sensor monitor the mixed supply water in real time, trimming the valve position to hold the setpoint precisely. This prevents thermal overshoot — critical for protecting timber and engineered-wood finishes — and reduces energy waste by ensuring the manifold never receives hotter water than needed.

Pressure & Temperature Gauges Included

Both pressure and temperature gauges are fitted as standard, giving an at-a-glance view of system status during commissioning and day-to-day operation. The unit also includes a dedicated air-vent port for straightforward bleeding during fill-up — no separate instruments needed.

Why a 1" Blending Valve?

A 1" bore handles significantly higher flow rates than a ¾" valve, suits multi-zone and larger floor areas, and its wider internal diameter minimises friction loss and pressure drop — allowing the Wilo Para to run at lower speed, saving energy and reducing noise. The more robust brass construction also delivers longer service life under continuous duty.

Wall-Mountable, Manifold-Ready Design

The complete mixing unit is engineered specifically for manifold installation with a lightweight, wall-mountable bracket for a tidy fit in plant rooms and airing cupboards. The G 1½" connections on both pump and blending valve match standard UFH manifold ports for a direct, no-adapter installation. A 5-year blending valve guarantee and 2-year pump guarantee underpin long-term confidence.

Honeywell V4043H Motorised 2-Port Zone Valve

The Honeywell V4043H is the installer-standard choice for zone control in domestic and light commercial underfloor heating systems. Available in 22 mm (HW2P-22) and 28 mm (HW2P-28) compression, it operates on a motor-open, spring-return principle — defaulting closed on power loss for inherent system protection. Key features include a potential-free SPST end switch to signal the boiler or pump, a manual lever for filling and draining without power, and a replaceable powerhead that can be swapped without draining the system.

Motor-Open, Spring-Return

The valve opens under electrical power and closes automatically by spring return when de-energised. This normally-closed, fail-safe design prevents unintended flow if power is lost, and ensures a clean shut-off whenever the zone thermostat is satisfied.

Potential-Free End Switch

The SPST potential-free end switch directly signals the boiler or circulating pump, firing the heat source only when a zone is genuinely calling — saving fuel and reducing wear. The 1 m heat-resistant flying lead wires cleanly into standard wiring centres and programmers.

Powerhead Replaceable Without Drain-Down

The powerhead can be removed and replaced in-situ without draining the system — a major time-saver on service calls. The integrated manual lever holds the valve open during filling, venting, or draining at commissioning.

Fast, Quiet Operation

Opening time is approximately 12 seconds under power; spring return takes around 6 seconds — fast enough to respond promptly to zone demand without water hammer. Low 6 W power consumption and a quiet synchronous motor mean no audible disturbance in occupied spaces.

Mixing Unit — Technical Specifications

Blending valve body material	Brass (HPB57-3)
Max working pressure	10 bar
Max media temperature	100 °C
Temperature control range	35–60 °C
Temperature control accuracy	±1 °C
Blending valve connection	1" (ISO 228 / G 1½")
Pump connection thread	G 1½"
Max system floor area	250 m²
Max heat output	20 kW
Pump power supply	230 V, 50 Hz
Blending valve guarantee	5 years
Pump guarantee	2 years

Wilo Para 25/6-43/SCU — Technical Specifications

Model	Wilo Para 25/6-43/SCU
Energy rating	Class A, ErP-compliant (EEI ≤ 0.21)
Max head	6 m
Power supply	230 V, 50/60 Hz
Port-to-port length	130 mm
Pipe connection	G 1½" (1.5" BSP)
Max operating pressure	10 bar
Control modes	Differential pressure proportional (Δp-v), differential pressure constant (Δp-c), 3× fixed speed
Motor type	EC (electronically commutated), glandless, maintenance-free
Starting torque	3× higher than comparable heating pumps
Self-controlled button	Yes (Green Button technology)
Differential pressure control	Integrated
Weight	2.8 kg
Compatible replacements	Wilo Gold Star, RS25/6, RS25/5, RS25-50, RS25-60, Yonos Pico 25/1-6-130, Yonos Pico 25/1-5-130

Honeywell V4043H — Technical Specifications

Valve type	2-port, normally closed, motor-open, spring-return
Connections available	22 mm compression (HW2P-22) / 28 mm compression (HW2P-28)
Power supply	230 V AC, 50 Hz
Power consumption	6 W
End switch type	SPST potential-free (22 mm) / SPDT (28 mm)
Switch rating	2.2 A
Opening time (nominal)	~12 seconds (under power)
Closing time (nominal)	~6 seconds (spring return)
Max static pressure	8.6 bar
Max differential pressure (close-off)	0.55 bar (22 mm) / 0.45 bar (28 mm)
Flow temperature range	5–88 °C
Ambient temperature range	5–50 °C
Kv (flow coefficient)	6.9 (22 mm) / 8.6 (28 mm)
Cable	1 m heat-resistant flying lead

Frequently Asked Questions

What floor area and heat output can this mixing set support?

The mixing unit is rated for systems up to 250 m² of floor area or 20 kW of heat output. The Wilo Para 25/6 delivers a max head of 6 m, which is sufficient for the vast majority of domestic UFH manifold layouts within those limits.

What makes the Wilo Para 25/6 energy efficient?

The Wilo Para uses an EC (electronically commutated) glandless motor with integrated differential pressure control, automatically adjusting speed to match system demand at any given moment. Its EEI ≤ 0.21 meets the ErP Class A benchmark, delivering major savings versus older fixed-speed pumps. The Green Button self-controlled technology means the pump can optimise itself without any external controller input.

Is the Wilo Para a direct replacement for older Wilo pumps?

Yes. The Wilo Para 25/6-43/SCU is a direct drop-in replacement for a wide range of older Wilo models including the Gold Star, RS25/6, RS25/5, RS25-50, RS25-60, Yonos Pico 25/1-6-130, and Yonos Pico 25/1-5-130 — all sharing the same 130 mm port-to-port length and G 1½" connections. It also offers 3× higher starting torque than comparable heating pumps, making it particularly reliable in systems with residual scale or where the pump has been idle.

What temperature does the blending valve control to, and how accurately?

The thermostatic blending valve controls supply water temperature between 35 °C and 60 °C with an accuracy of ±1 °C. This range covers all standard UFH applications — from low-temperature heat pump outputs (~35–45 °C) to higher-temperature boiler systems — and the integrated sensor and controller continuously adjust the valve to maintain the setpoint.

Do I need a 2-port zone valve, and which size should I choose?

A 2-port motorised zone valve is needed for each independently controlled heating zone. The Honeywell V4043H 22 mm suits most domestic pipework and is the standard choice for UFH systems. The 28 mm version is used where higher flow rates are required — typically larger domestic or light commercial systems. Both feature a potential-free end switch to fire the boiler or pump only when that zone calls for heat.

Can the Honeywell V4043H powerhead be serviced without draining down?

Yes. The V4043H powerhead is designed to be removed and replaced in-situ without draining the system. The manual lever allows the valve to be held open during initial fill-up and system venting, and can also be used to isolate a zone manually if needed during maintenance — a significant time-saver on service visits.

Manifolds & Kits