BoilerFaultCodesVaillant F22 Fault Code
The Vaillant F22 fault code means: your boiler has stopped working because the water pressure is too low for it to run safely.. It appears on 11 Vaillant models in our database.
Technical description: Insufficient water in the system
What causes the Vaillant F22 fault?
This fault occurs when the internal sensors detect that there isn't enough water circulating through the boiler to operate safely. The most common reason is a slow leak somewhere in your radiator system or a failing component that has allowed pressure to drop below the minimum threshold. Without enough water, the boiler shuts down to prevent the heat exchanger from overheating.
This issue is frequently seen in autumn when homeowners turn their heating back on for the first time, as tiny leaks during the summer months can gradually drain the system pressure.
DIY fix possible
Check the pressure gauge on the front of the boiler; it is likely below 1 bar.Locate the external filling loop, which is usually a flexible silver hose under the boiler.Slowly open the tap valves on the hose until the gauge reaches 1.5 bar, then close them tightly.Reset the boiler to clear the fault code.
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Vaillant models that show the F22 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoTEC Plus 615 Repair: £80-150
- ecoTEC Plus 620 Repair: £0-120
- ecoTEC Plus 625 Repair: £0-120
- ecoTEC Plus 630 Repair: £0-120
- ecoTEC Plus 635 Repair: £0-120
- ecoTEC Plus 840 Repair: £0-120
- ecoTEC Plus 938 Repair: £0-120
- ecoTEC sustain Repair: £0-120
- Home Combi Repair: £90-180
- Home System Repair: £0-160
- Thermocompact Repair: £0-120
Source
Vaillant F22 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoTEC Plus 840 manual (PDF)
- Vaillant ecoTEC Plus 938 manual (PDF)
- Vaillant ecoTEC sustain manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026