High
F.33 on Vaillant Home System

Your boiler has identified a problem with how it moves air and fumes through the system, preventing it from starting safely.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Fanfrostprotectionfunctionactive:Airpressureswitchfault Pressuremonitorhasnotswitchedorhasswitchedatafanspeedvaluethatisistoohigh(insufficientairsupply) Pressuremonitorplugnotcorrectlypluggedin,pressuremonitordefective,lineremovedfrombetweenthepressuremonitorandsilencer,air/fluepipeblockedandsilencernotinstalledproperly

From this model's manual
Verified against the Vaillant Home System installation & service manual, page 34.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.32View →S.33View →

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