How to Replace the Pcb on a Main Eco Compact 25 (UK)
Step-by-step UK guide to replacing the printed circuit board on a Main Eco Compact 25. Part numbers, torques, commissioning.
The part
Replace the main control PCB — the most common cause of no-heat, no-DHW and intermittent lockouts on Main Eco Compact 25.
Isolate safely
Isolate at the fused spur and lock off. Discharge any residual mains voltage before touching connectors.
Fit and commission
Photograph every plug and its position on the Main Eco Compact 25 PCB before unclipping — connector positions differ subtly across firmware revisions.
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
- PCB part number location?
- On Main Eco Compact 25 the PCB label is on the top-right of the board, printed as an 7734-series code. Match every digit.
- Do I need to re-parameterise?
- Yes — enter the correct boiler model code in the service menu after fitting so the ignition curve, fan speed and gas rate match.
- 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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