BoilerFaultCodesBaxi 40 Fault Code
The Baxi 40 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water coming back from your radiators, preventing it from heating your home properly.. It appears on 18 Baxi models in our database.
Technical description: Central Heating Return NTC Fault
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 →Avoid the next call-out bill
A cover plan would handle faults like 40: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Baxi models that show the 40 fault code
Click a model for the full fault code list and model-specific repair notes.
- 124 Combi Repair: £90-160
- 200 / 400 Combi Repair: £120-200
- 600 Combi (range) Repair: £90-160
- 624 Combi Repair: £90-160
- 825 Combi Repair: £90-160
- Assure Repair: £150-300
- Bahama 100 Repair: £150-300
- Combi Instant 80/105 HE Repair: £120-220
- Duo-tec Combi GA Repair: £90-160
- Duo-tec Combi HE A Repair: £120-200
- EcoBlue Repair: £120-200
- Ecoblue Advance Combi Repair: £120-220
- EcoBlue Advance Heat Repair: £90-160
- EcoBlue Heat Repair: £90-160
- EcoBlue Plus Combi Repair: £100-180
- EcoBlue System Repair: £120-200
- Solo 3 Repair: £120-250
- Solo 3 PFL Repair: £150-300
Source
Baxi 40 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026