How to Replace the Pcb on a Viessmann Vitodens 100-W 35 (UK)
Step-by-step UK guide to replacing the printed circuit board on a Viessmann Vitodens 100-W 35. Part numbers, torques, commissioning.
The part
Replace the main control PCB — the most common cause of no-heat, no-DHW and intermittent lockouts on Viessmann Vitodens 100-W 35.
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 Viessmann Vitodens 100-W 35 PCB before unclipping — connector positions differ subtly across firmware revisions.
Recommission checklist
Refill the Viessmann Vitodens 100-W 35 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 Viessmann Vitodens 100-W 35 the PCB label is on the top-right of the board, printed as an 7828-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 Viessmann Vitodens 100-W 35 is in warranty — Viessmann require log of any part swap for labour claims.
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