BoilerFaultCodesHalstead Overheat thermostat activated Fault Code
Also written as OVERHEATTHERMOSTATACTIVATED — same fault.
The Halstead Overheat thermostat activated fault code means: your boiler has switched itself off because it has become dangerously hot, likely due to a circulation problem or a faulty safety sensor.. It appears on 1 Halstead model in our database.
Technical description: Boiler temperature > 105°C • Check CH/O’heat thermistor • Check wires to sensor • Check no air is in CH system • Check PCB • Check pump
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 →Avoid the next call-out bill
A cover plan would handle faults like Overheat thermostat activated: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Halstead models that show the Overheat thermostat activated fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Halstead Overheat thermostat activated fault code information on this page is sourced and cross-checked against the official Halstead service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026