BoilerFaultCodesAlpha 46 Fault Code
The Alpha 46 fault code means: your boiler has stopped running because an external safety thermostat has detected that the water temperature has become too hot.. It appears on 21 Alpha models in our database.
Technical description: Optional thermostat intervention
What causes the Alpha 46 fault?
This fault occurs when an external safety device triggers to prevent the system from getting dangerously hot. It usually happens because water is not moving through the boiler quickly enough, often due to a pump failure or a blockage in the heating pipes. When the heat cannot be carried away from the boiler, the temperature spikes and the safety thermostat cuts the power to prevent damage.
This issue is more frequent during the first cold spell of autumn when a pump that has been idle all summer fails to start up again.
DIY fix possible
Check that your pump is running and hasn't seizedEnsure all radiator valves and boiler service valves are fully openPress the 'Reset' button on the front of the boiler control panel
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Alpha models that show the 46 fault code
Click a model for the full fault code list and model-specific repair notes.
- C25 Xtraflame Repair: £120-250
- E-Tec Repair: £80-150
- E-Tec 24 Repair: £80-150
- E-Tec 28 Repair: £80-150
- E-Tec 33 Repair: £80-150
- E-Tec Plus Repair: £100-200
- E-Tec Plus 24 Repair: £100-200
- E-Tec Plus 28 Repair: £100-200
- E-Tec Plus 33 Repair: £100-200
- E-Tec R Repair: £100-200
- E-Tec Regular Repair: £80-180
- Eco Repair: £90-180
- Eco 11 13 Repair: £90-180
- FMK Repair: £90-180
- H25 Xtraflame Repair: £120-250
- Intec 24GS Repair: £120-200
- Intec 28GS Repair: £120-250
- Intec 40GS2 Repair: £90-180
- Intec 50CS Repair: £120-250
- Intec2 25 28XE Repair: £80-150
- Intec2 30SE Repair: £120-250
Source
Alpha 46 fault code information on this page is sourced and cross-checked against the official Alpha service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026