BoilerFaultCodesTechnical description
Overheat thermostat trip. Possible causes: system not pressurised, air in system, bypass not fitted/adjusted, pump failure, or sensor/thermistor fault.
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to shut the system down. The most common reasons are a lack of water pressure, a failing pump that isn't moving heat away from the boiler quickly enough, or trapped air pockets causing the unit to spike in temperature.
This issue often appears when the heating is first turned on in autumn, as circulation pumps can seize up after being idle throughout the summer.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.