BoilerFaultCodesTechnical description
Overheat cut off device tripped or thermostat, overheat cut off device faulty
What causes this fault?
This fault occurs when the water inside your boiler reaches an unsafe temperature, triggering a safety switch to cut the power. It is often caused by a failing pump that can no longer move heat away from the boiler quickly enough or a buildup of limescale and sludge that restricts water flow. In some cases, the safety sensor itself may have developed a fault and is wrongly reporting that the unit is overheating.
This issue often surfaces when you first turn your heating back 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.