BoilerFaultCodesWorcester Bosch A5 Fault Code
The Worcester Bosch A5 fault code means: your boiler's temperature sensor responsible for monitoring the hot water storage is faulty or has lost connection, meaning the system cannot safely heat your water.. It appears on 13 Worcester Bosch models in our database.
Technical description: Tank (Heat Bank) NTC sensor defective.
What causes the Worcester Bosch A5 fault?
This fault occurs when the internal sensor responsible for monitoring the temperature of your stored hot water fails to send a clear signal to the main control board. The most common reason is that the sensor has developed an internal electrical fault or its wiring has become loose or corroded over time. Because the boiler no longer knows how hot the water is, it shuts down as a safety precaution to prevent 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 →Worcester Bosch models that show the A5 fault code
Click a model for the full fault code list and model-specific repair notes.
- CDi Highflow Repair: £150-250
- Greenstar 25 HE Combi Repair: £90-160
- Greenstar 25HE Repair: £90-160
- Greenstar 25i (ZWB 7-25) Repair: £150-250
- Greenstar CDi Compact Repair: £100-£180
- Greenstar R29 40 HE Repair: £120-220
- Highflow 250 Repair: £150-250
- Highflow 300 Repair: £150-250
- Highflow 440 CDi Repair: £150-250
- Highflow 550 CDi Repair: £150-250
- Ri 25 HE Repair: £120-220
- WR325 RSF Repair: £180-350
- ZB 7 27 HE Repair: £150-250
Source
Worcester Bosch A5 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026