Technical description
Temperature anomaly
What causes this fault?
This fault occurs when the boiler detects a rapid rise in temperature because water isn't moving through the system quickly enough. The most common reasons are a failing circulation pump that can't push the water round, or a sensor that has become faulty and is giving the boiler an incorrect reading.
This issue often surfaces in autumn when the heating is turned back on for the first time, as internal pump components can seize up after being idle during 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.