BoilerFaultCodesTechnical description
Maximum difference failure between 2 NTC temperature sensor – poor circulation.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is heating up too quickly or not flowing away from the heat exchanger fast enough. The most common reasons are a failed or blocked circulation pump, air trapped in the system, or a buildup of sludge and debris that has restricted the internal pipework. Because the heat cannot be moved into your radiators effectively, the boiler shuts down to prevent the unit from overheating.
This issue is most frequently seen at the start of autumn when the heating is turned back on after being idle 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.