BoilerFaultCodesTechnical description
Temperature difference between flow and return too large
What causes this fault?
This fault occurs when water is unable to move through the boiler fast enough to carry heat away, causing a dangerous temperature buildup. The most common reasons are a failed internal pump that has stopped spinning or a heavy buildup of sludge and debris that is physically blocking the pipework. It can also be caused by air trapped in the system or sensors that are sending incorrect readings to the control board.
This issue often appears when you first turn the heating back on in autumn, as moving parts can seize and debris can settle during the summer months 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.