BoilerFaultCodesTechnical description
Maximum difference between T1 and T2 exceeded
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the outgoing water is significantly hotter than the returning water, suggesting a lack of circulation. The most common reason is a failed or stuck pump, though it can also be triggered by air trapped in the system or a blockage in the pipework. In some cases, a build-up of sludge or debris within the heat exchanger prevents the water from moving through the boiler fast enough to carry the heat away.
This fault often appears during the first few cold days of autumn when a pump that has been idle all summer fails to spin back up.
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.