BoilerFaultCodesVaillant D.24 Fault Code
Also written as D24 — same fault.
The Vaillant D.24 fault code means: your boiler is struggling with water circulation, likely because the internal pump is not working properly or there is an air lock in the system.. It appears on 27 Vaillant models in our database.
Technical description: Check diagnostic code. Check external controls are calling for heat (also see note A sheet 1). Repair or replace as necessary.
What causes the Vaillant D.24 fault?
This fault occurs when the boiler detects that water isn't moving through the heat exchanger as fast as it should. The most common reasons are a failing internal pump that can no longer push the water around or a large pocket of air trapped in the system blocking the flow.
This issue is frequently seen in autumn when the heating is turned back on for the first time after summer, as pumps can seize during long periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A cover plan would handle faults like D.24: no call-out fees, no surprise bills.
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Vaillant models that show the D.24 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £0-120
- ecoFIT Pure 418 Repair: £0-120
- ecoFIT Pure 425 Repair: £80-160
- ecoFIT Pure 435 Repair: £30-150
- ecoFIT Pure 825
- ecoFIT Pure 830
- ecoFIT Pure 835 Repair: £0-120
- ecoMAX Repair: £250-450
- ecoMAX 613 Repair: £150-300
- ecoMAX 618 Repair: £150-300
- ecoMAX 622 Repair: £150-300
- ecoMAX 635 Repair: £150-300
- ecoMAX 824E Repair: £150-300
- ecoMAX 828E Repair: £120-250
- Ecomax Condensing 600/800 series Repair: £150-300
- ecoMAX System 612 Repair: £150-300
- ecoTEC plus aquaPLUS Repair: £120-£280
- Home Combi Repair: £120-250
- Home System Repair: £0-120
- Thermocompact Repair: £180-£350
- Turbomax 824/828 Repair: £150-250
- Turbomax Plus Repair: £150-£300
- Turbomax Plus 824/828E
- Turbomax Plus 828 Repair: £60-140
- Turbomax Plus 828 E
- Turbomax Plus VUW 242E
- Turbomax Plus VUW 242EH
Source
Vaillant D.24 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