BoilerFaultCodesTechnical description
Requires reset – temperature measured by return sensor greater than flow temperature.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water coming back from your radiators is hotter than the water being sent out, which contradicts the laws of physics in a standard heating cycle. The most common reason is a lack of water flow caused by a failing pump or a blockage, but it can also be triggered if one of the temperature sensors has become faulty and is sending incorrect data to the control board.
This issue often surfaces during the first cold spell of autumn when the heating system is turned on after being dormant all summer, which can cause the internal pump to seize.
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.