BoilerFaultCodesTechnical description
Error with return line probe – over temperature outlet or differential alarm
What causes this fault?
This fault occurs when the internal sensors detect that the water returning from your heating system is significantly hotter than expected or is rising too quickly. The most common reasons are a blockage in the central heating pipes, a failing pump that isn't moving water efficiently, or a sensor that has become faulty and is sending incorrect data to the boiler's computer.
This issue is most frequent during the first cold spell of autumn when heating systems are turned back on after months of inactivity, often revealing stuck pumps or airlocks.
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.