BoilerFaultCodesVaillant F70 Fault Code
The Vaillant F70 fault code means: your boiler's computer parts are not communicating correctly because they haven't been told which specific model of boiler they are installed in.. It appears on 13 Vaillant models in our database.
Technical description: When replacing both components [display and electronics], after being turned on, the appliance goes to fault and displays the error message “F70”.
What causes the Vaillant F70 fault?
This fault occurs when the boiler's internal computer boards lose their identity and no longer know which specific model they are controlling. It most commonly happens after a repair where new parts have been fitted but haven't been digitally linked to the boiler's unique settings. Without this specific configuration code, the system shuts down as a safety precaution because it doesn't know its own power rating or technical limits.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the F70 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoTEC Repair: £80-160
- ecoTEC plus Repair: £80-120
- ecoTEC Plus 615 Repair: £80-120
- ecoTEC Plus 620 Repair: £80-120
- ecoTEC Plus 625 Repair: £80-120
- ecoTEC Plus 630 Repair: £80-120
- ecoTEC Plus 635 Repair: £80-120
- ecoTEC Plus 65 Repair: £80-120
- ecoTEC Plus 832 Repair: £80-120
- ecoTEC Plus 836 Repair: £80-120
- ecoTEC Plus 840 Repair: £80-120
- ecoTEC Plus 938 Repair: £80-120
- ecoTEC sustain Repair: £80-120
Source
Vaillant F70 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