BoilerFaultCodesVaillant D.24 Fault Code
Also written as D24 — same fault.
The Vaillant D.24 fault code means: your boiler is struggling with water flow, likely due to a build-up of debris or air in the system which is preventing the heat from circulating properly.. It appears on 32 Vaillant models in our database.
Technical description: Not relevant
What causes the Vaillant D.24 fault?
This fault occurs when the boiler's internal temperature rises too quickly because the heated water cannot move away from the heat exchanger fast enough. The most common cause is a blockage from sludge or trapped air pockets that restrict the flow, forcing the boiler to throttle back or stop to prevent overheating.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as settled debris in the pipes can shift and block the pump.
DIY fix possible
Check that all radiator valves are fully openBleed your radiators to remove any trapped airEnsure the boiler pressure is between 1.0 and 1.5 bar on the gauge
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the D.24 fault code
Click a model for the full fault code list and model-specific repair notes.
- aquaPLUS Repair: £120-£280
- Atmomax Repair: £0-120
- Combi Compact 242EB Repair: £0-120
- Combi Compact 282EB Repair: £60-180
- ecoFIT pure Repair: £0-120
- ecoFIT Pure 412 Repair: £120-200
- ecoFIT Pure 418 Repair: £0-120
- ecoFIT Pure 425 Repair: £80-160
- ecoFIT Pure 435 Repair: £30-150
- ecoFIT Pure 835 Repair: £0-120
- ecoTEC Repair: £80-250
- ecoTEC plus Repair: £150-£300
- ecoTEC Plus 615 Repair: £150-£300
- ecoTEC Plus 620 Repair: £150-£300
- ecoTEC Plus 625 Repair: £150-£300
- ecoTEC Plus 630 Repair: £150-£300
- ecoTEC Plus 635 Repair: £150-£300
- ecoTEC Plus 65 Repair: £150-£300
- ecoTEC Plus 832 Repair: £150-£300
- ecoTEC Plus 836 Repair: £150-£300
- ecoTEC Plus 840 Repair: £150-£300
- ecoTEC Plus 938 Repair: £150-£300
- ecoTEC plus Aquaplus Repair: £150-300
- ecoTEC plus System Repair: £120-250
- ecoTEC sustain Repair: £150-£300
- Home System Repair: £0-120
- Thermocompact Repair: £180-£350
- 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.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026