BoilerFaultCodesTechnical description
Temperature difference between the supply sensor and return sensor too large.
What causes this fault?
This fault occurs when the heat generated by the burner isn't being carried away to your radiators quickly enough, causing heat to build up inside the unit. The most common reason is a failing pump that can no longer push the water around your home, though a blockage caused by sludge or debris in the system can also restrict this flow. If the water stays inside the boiler for too long, it overheats and the system shuts down for safety.
This fault often appears during the first cold spell of autumn when the heating is turned on after being dormant all summer, as pumps often seize up 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.