BoilerFaultCodesWorcester Bosch 1021 Fault Code
The Worcester Bosch 1021 fault code means: your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps aren't getting hot enough or stay cold.. It appears on 10 Worcester Bosch models in our database.
Technical description: Cylinder charging or hot water temperature sensor faulty
What causes the Worcester Bosch 1021 fault?
This fault occurs when the boiler's internal computer stops receiving a reliable signal from the sensors that monitor your hot water temperature. The most common reason is that the sensor has either worn out internally or a connection in the wiring has become loose or corroded, preventing the boiler from knowing when to fire up to heat your water.
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 1021 fault code
Click a model for the full fault code list and model-specific repair notes.
- 1000 Repair: £120-200
- Greenstar 2000 Repair: £120-220
- Greenstar 27CDi Repair: £120-220
- Greenstar 28CDi Repair: £120-220
- Greenstar 4000 Repair: £120-220
- Greenstar 8000 Repair: £120-220
- Greenstar 8000 Life Repair: £120-220
- Greenstar 8000 Life System Repair: £120-200
- Greenstar 8000 Life/Style Repair: £110-180
- Greenstar 8000 Style Repair: £120-220
Source
Worcester Bosch 1021 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