BoilerFaultCodesIntergas 21 Fault Code
The Intergas 21 fault code means: your boiler has detected a problem with the temperature sensor that monitors the water returning to the unit, causing it to stop running for safety.. It appears on 11 Intergas models in our database.
Technical description: Sensor fault S2
What causes the Intergas 21 fault?
This fault occurs when the boiler's internal computer stops receiving a reliable temperature reading from the sensor on the return pipe. It is usually caused by the sensor itself failing, or a loose connection in the wiring that prevents the signal from reaching the control board. For safety, the boiler shuts down because it can no longer monitor if the water returning from your radiators is at a safe temperature.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Intergas models that show the 21 fault code
Click a model for the full fault code list and model-specific repair notes.
- Combi Compact ECO RF Repair: £90-180
- Combi Compact HRE Repair: £120-220
- Combi Compact HRE 24/18 Repair: £90-180
- Combi Compact HRE 28/24 Repair: £90-180
- Combi Compact HRE 36/30 Repair: £90-180
- Combi Compact HRE SB Repair: £90-180
- Compact HRE OV Repair: £120-190
- Rapid Repair: £120-220
- Rapid 25 Repair: £90-180
- Rapid 25 32 Repair: £90-180
- Rapid 32 Repair: £90-180
Source
Intergas 21 fault code information on this page is sourced and cross-checked against the official Intergas service / installation manuals for each affected model.
- Intergas Combi Compact ECO RF manual (PDF)
- Intergas Combi Compact HRE manual (PDF)
- Intergas Combi Compact HRE 36/30 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026