Emergency
F.33 on Vaillant ecoTEC plus System

Your boiler has detected an issue with its airflow system, meaning it cannot safely vent exhaust gases, so it has shut down to prevent a fire or carbon monoxide risk.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description

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

Engineer required

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

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.32View →F.67View →

Related guides you might find useful

Boiler keeps losing pressure

Six most common causes of dropping pressure.

Read →

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →