BoilerFaultCodesTechnical description
FAULT POINT F. Primary water too hot (over 85°C) or too low (less than 75°C). Possible causes: thermistor/heat paste fault, low gas pressure, blocked flue/heat exchanger/burner, or gas valve sticking.
What causes this fault?
This fault occurs when the internal sensors detect that the water temperature has strayed outside of its safe operating window, usually due to a lack of circulation or incorrect heat levels. The most common reason is a failing temperature sensor (thermistor) providing inaccurate readings, or a blockage within the heat exchanger that prevents heat from transferring correctly. In some cases, a fault with the gas valve or the main control board can cause the burner to stay on too long, leading to overheating.
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.