BoilerFaultCodesWorcester Bosch Ad Fault Code
Also written as AD — same fault.
The Worcester Bosch Ad fault code means: your boiler is having trouble communicating with the sensor that monitors the temperature of your hot water cylinder.. It appears on 13 Worcester Bosch models in our database.
Technical description: Cylinder temperature sensor (NTC) not recognized
What causes the Worcester Bosch Ad fault?
This fault occurs when the boiler's main control board loses the electrical connection to the sensor responsible for monitoring your hot water tank’s temperature. The most common reason is that the sensor itself has developed an internal fault or the wiring connecting it to the boiler has become loose or damaged over time.
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 Ad fault code
Click a model for the full fault code list and model-specific repair notes.
- 537i Repair: £90-180
- Greenstar 25 HE Combi Repair: £120-220
- Greenstar 25HE Repair: £90-180
- Greenstar 25i (ZWB 7-25) Repair: £120-200
- Greenstar 30HE Repair: £90-160
- Greenstar R29 40 HE Repair: £100-200
- 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: £150-300
- WR325 RSF Repair: £90-180
- ZB 7 27 HE Repair: £120-220
Source
Worcester Bosch Ad 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