BoilerFaultCodesTechnical description
DIFF GREATER THAN 50°C CHECK ISOLATION VALVES ARE OPEN CHECK PUMP CHECK RAD VALVES OPEN CHECK SYSTEM BLOCKAGES
What causes this fault?
This fault happens when heat cannot escape the boiler quickly enough, causing the internal temperature to spike dangerously fast. It is usually caused by a pump failure that stops water from moving or a blockage in the pipes, such as a buildup of sludge or closed valves, that prevents circulation. Effectively, the boiler is producing heat but has nowhere to send it, so it shuts down to prevent damage.
This issue often appears when the heating is turned back on for autumn, as 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.