BoilerFaultCodesAlpha 12 Fault Code
The Alpha 12 fault code means: your boiler has lost connection with the sensor that monitors the temperature of your hot water cylinder, meaning it may not know when to heat your water.. It appears on 25 Alpha models in our database.
Technical description: Cylinder sensor fault (FlowSmart only)
What causes the Alpha 12 fault?
This fault occurs when the main control board can no longer detect an electrical signal from the temperature probe attached to your hot water tank. It is usually caused by the sensor internal components failing over time or a loose connection in the wiring that links the cylinder to the boiler.
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 →Alpha models that show the 12 fault code
Click a model for the full fault code list and model-specific repair notes.
- 240XE Repair: £120-250
- C25 Xtraflame Repair: £120-220
- E-Tec Repair: £120-200
- E-Tec 24 Repair: £120-200
- E-Tec 28 Repair: £120-200
- E-Tec 33 Repair: £120-200
- E-Tec Plus Repair: £120-250
- E-Tec Plus 10 / 18 Repair: £90-160
- E-Tec Plus 24 Repair: £120-250
- E-Tec Plus 28 Repair: £120-250
- E-Tec Plus 33 Repair: £120-250
- E-Tec R Repair: £120-220
- E-Tec Regular Repair: £90-160
- Eco Repair: £120-220
- Eco 11 13 Repair: £90-180
- Evoke Repair: £120-200
- Evoke 10 / 18 Repair: £90-160
- FMK Repair: £90-180
- H25 Xtraflame Repair: £120-220
- Intec 24GS Repair: £120-220
- Intec 28GS Repair: £120-220
- Intec 40GS2 Repair: £120-220
- Intec 50CS Repair: £120-220
- Intec2 25 28XE Repair: £120-250
- Intec2 30SE Repair: £120-250
Source
Alpha 12 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