BoilerFaultCodesBaxi ON FLASH ON Fault Code
Also written as ONFLASHON — same fault.
The Baxi ON FLASH ON fault code means: your boiler has detected a problem with its internal temperature sensor and has stopped working as a safety precaution.. It appears on 24 Baxi models in our database.
Technical description: Thermistor error
What causes the Baxi ON FLASH ON fault?
This fault occurs when the boiler's internal temperature sensor, known as a thermistor, fails to send a reliable signal to the main control board. The most common reason is that the sensor has developed an electrical fault or has simply worn out over time, meaning it can no longer accurately monitor the water temperature. As a result, the boiler shuts down to prevent itself from overheating.
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 →Baxi models that show the ON FLASH ON fault code
Click a model for the full fault code list and model-specific repair notes.
- 130 HE (range) Repair: £90-180
- 400 Combi (range) Repair: £90-160
- 800 Repair: £90-180
- 80e Repair: £90-160
- Assure Repair: £100-180
- Bermuda Repair: £90-160
- Eco Compact Repair: £90-160
- Eco Elite Repair: £90-160
- EP Repair: £90-160
- Netaheat Repair: £120-220
- Performa Repair: £90-160
- Profile Repair: £90-160
- Profile Prima Repair: £100-180
- Solo Repair: £100-£180
- Statesman Repair: £90-160
- Suprima 100 Repair: £90-160
- Suprima 115 Repair: £100-£190
- Suprima 30 Repair: £90-180
- Suprima 40 Repair: £120-220
- Suprima 50 Repair: £120-190
- Suprima 60 Repair: £120-220
- Suprima 70 Repair: £90-160
- Suprima 80 Repair: £90-180
- Titanium Repair: £90-160
Source
Baxi ON FLASH ON 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 27 April 2026