PCB part number location?

On Baxi 800 Combi 36 the PCB label is on the top-right of the board, printed as an 720-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.

Only if the Baxi 800 Combi 36 is in warranty — Baxi require log of any part swap for labour claims.

Replace the main control PCB — the most common cause of no-heat, no-DHW and intermittent lockouts on Baxi 800 Combi 36.

Isolate at the fused spur and lock off. Discharge any residual mains voltage before touching connectors.

Photograph every plug and its position on the Baxi 800 Combi 36 PCB before unclipping — connector positions differ subtly across firmware revisions.

Refill the Baxi 800 Combi 36 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.

PCB part number location?: On Baxi 800 Combi 36 the PCB label is on the top-right of the board, printed as an 720-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 Baxi 800 Combi 36 is in warranty — Baxi require log of any part swap for labour claims.

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