How much does it cost to fix Vaillant error code F.35?

Typical repair cost for the Vaillant F.35 fault is £150-350 including labour.

F.35 Emergency

Vaillant F.35 Fault Code

Q: What does the Vaillant F.35 fault code mean?

Your boiler is having trouble breathing because there may be a blockage, damage, or an obstruction in the pipework that vents exhaust gases outside.

Also written as F35 — same fault.

The Vaillant F.35 fault code means: your boiler is having trouble breathing because there may be a blockage, damage, or an obstruction in the pipework that vents exhaust gases outside.. It appears on 1 Vaillant model in our database.

Technical description: Fault:Air/fluegasduct Checktheentireair/fluepipefor: – Permitteddesign – Restrictionorblockageintheair/fluepipecausedbyobstructions – Damage

Typical repair cost £150-350 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the F.35 fault code

Click a model for the full fault code list and model-specific repair notes.

ecoTEC exclusive Repair: £150-350

Source

Vaillant F.35 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026