BoilerFaultCodesGrant Overheat thermostat Fault Code
Also written as OVERHEATTHERMOSTAT — same fault.
The Grant Overheat thermostat fault code means: your boiler has switched itself off because it has become dangerously hot, likely due to a circulation problem or a system blockage.. It appears on 10 Grant models in our database.
Technical description: Automatically switch off the boiler if the heat exchanger exceeds a pre-set temperature of 111°C ± 3°C.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Grant models that show the Overheat thermostat fault code
Click a model for the full fault code list and model-specific repair notes.
- Euroflame Repair: £120-250
- Outdoor Combi 90 Mkii Repair: £90-180
- Vortex 15-20 Repair: £150-300
- Vortex 20-26 Repair: £150-300
- Vortex Eco Repair: £150-300
- Vortex Eco External Floor Standing Repair: £150-300
- Vortex Eco External Wall Hung Repair: £150-300
- Vortex Pro 15-26 Repair: £150-300
- Vortex Pro Combi Repair: £120-250
- Vortex Pro Combi 26 Repair: £120-250
Source
Grant Overheat thermostat fault code information on this page is sourced and cross-checked against the official Grant service / installation manuals for each affected model.
- Grant Euroflame manual (PDF)
- Grant Outdoor Combi 90 Mkii manual (PDF)
- Grant Vortex 15-20 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026