Medium
S.40 on Vaillant Combi Compact 242EB

Your boiler has detected an internal issue and is running at a lower power level to keep providing some heat while protecting itself from damage.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Comfort safety mode active

DIY fix possible

Check that all radiator valves are fully openEnsure the boiler pressure gauge is between 1.0 and 1.5 barPress the 'Reset' button (flame symbol with a cross) and wait for the boiler to restart

Find a Gas Safe engineer
Search the official register →

Related fault codes

F.20View →F.22View →F.24View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Radiators cold at the bottom

Sludge build-up — needs flushing, not bleeding.

Read →