High
22.D on Vaillant Thermocompact

Your boiler's computer has detected a potential communication error or a generic system check failure, meaning it has safely switched itself off to prevent a fault from worsening.

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

Diagnostic code check

From this model's manual
Verified against the Vaillant Turbomax Plus 824 828e installation & service manual.
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.22View →F.23View →

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