How to Replace the Diverter Valve on a Main Eco Compact 25 (UK)
Step-by-step UK guide to replacing the 3-way diverter valve on a Main Eco Compact 25. Part numbers, torques, commissioning.
The part
Replace the diverter valve on Main Eco Compact 25 when hot water runs cold on demand or the boiler cycles between CH and DHW.
Isolate safely
Drain to below the diverter body via the CH drain-off. On Main Eco Compact 25 the diverter is a cartridge design — pull the retaining clip and lift out.
Fit and commission
Fit new O-rings, silicone-grease the cartridge and align the actuator drive slot before refitting the motor.
Recommission checklist
Refill the Main Eco Compact 25 to 1.2 bar cold. Bleed high-point radiators and the internal AAV.
Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.
Frequently asked questions
- Actuator or cartridge only?
- Diagnose first: manually push the actuator pin. If it moves freely, replace the actuator only; if the pin sticks, the cartridge is scaled.
- Any special tools?
- A brass spanner or the OEM diverter tool avoids cracking the plastic body on Main Eco Compact 25.
- Do I need to notify the manufacturer?
- Only if the Main Eco Compact 25 is in warranty — Main require log of any part swap for labour claims.
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