BoilerFaultCodesVaillant D.70 Fault Code
Also written as D70 — same fault.
The Vaillant D.70 fault code means: your boiler is currently stuck in a diagnostic test mode that overrides its normal settings, which usually happens during a service or repair.. It appears on 19 Vaillant models in our database.
Technical description: Set diverter valve position
What causes the Vaillant D.70 fault?
This code appears because the boiler has been manually instructed to hold its internal diverter valve in a specific position for testing purposes. This usually happens during a professional service when a technician needs to isolate the heating or hot water circuits to check for leaks or performance issues. If the code remains on the screen, the boiler has simply not been exited out of this specific diagnostic menu.
DIY fix possible
Locate the display panel on the front of the boilerPress the 'Reset' button (marked with a flame or cross symbol) for one secondWait for the boiler to restart and check if the 'D.70' code has disappeared
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.70 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax
- Combi Compact 242EB Repair: £0-90
- Combi Compact 282EB Repair: £100-250
- ecoTEC Repair: £0-90
- ecoTEC plus
- ecoTEC Plus 615
- ecoTEC Plus 620
- ecoTEC Plus 625
- ecoTEC Plus 630
- ecoTEC Plus 635
- ecoTEC Plus 65
- ecoTEC Plus 832
- ecoTEC Plus 836
- ecoTEC Plus 840
- ecoTEC Plus 938
- ecoTEC plus Regular Repair: £0-80
- ecoTEC plus System
- ecoTEC sustain
- Home System Repair: £0-80
Source
Vaillant D.70 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