BoilerFaultCodesVaillant D.22 Fault Code
Also written as D22 — same fault.
The Vaillant D.22 fault code means: your boiler is currently preparing or delivering hot water, which is a normal operating status of the pre-heat function rather than a failure.. It appears on 37 Vaillant models in our database.
Technical description: Check diagnostic code. (turboMAX Plus only) check diverter valve spindle against blade lightly. Replace diverter valve.
What causes the Vaillant D.22 fault?
This status occurs when the boiler's internal pre-heat function, known as Warmstart, is active to ensure hot water is available quickly. It is triggered either by the boiler periodically heating its own internal store or when you turn on a hot water tap. This is part of the appliance's normal operation and indicates the system is working as intended to maintain comfort.
DIY fix possible
Check if the hot water tap is currently runningTurn off the 'Warmstart' comfort function using the dial if you do not want the boiler to fire periodically to keep water hotMonitor the display to see if it switches back to a heating or standby code once the demand ends
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Vaillant models that show the D.22 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax
- ecoFIT Pure 418
- ecoFIT Pure 425
- ecoFIT Pure 435
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835
- ecoMAX
- ecoMAX 613
- ecoMAX 618
- ecoMAX 622
- ecoMAX 635
- ecoMAX 824E
- ecoMAX 828E
- Ecomax Condensing 600/800 series
- ecoMAX System 612
- ecoTEC
- ecoTEC 65kW Repair: £120-250
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 840
- ecoTEC plus aquaPLUS
- ecoTEC Pro / ecoTEC Plus
- ecoTEC sustain
- Home Combi
- Home System
- Thermocompact
- Turbomax 824/828
- Turbomax Plus
- Turbomax Plus 824/828E
- Turbomax Plus 828 Repair: £0-120
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant D.22 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoMAX manual (PDF)
- Vaillant ecoMAX System 612 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026