BoilerFaultCodesTechnical description
Boiler Max temperature exceeded for gradient (or overtemperature) Probable pump jammed or air in the circuit or Safety thermostat sensor tripped
What causes this fault?
This fault happens when the water inside the boiler gets too hot too quickly, triggering a safety shut-off to prevent damage. It is usually caused by a blockage or a pump failure that stops the water from moving through the system and carrying the heat away. Common culprits include a seized pump, a buildup of air in the pipes, or a physical blockage like limescale or sludge.
This fault is frequently seen in autumn when the heating is turned on for the first time after summer, as the internal pump can become seized during long periods of inactivity.
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.