BoilerFaultCodesWhat the manual says
Manufacturer manualwaiting time: temperature difference flow - return sensor too high (Check thermistor fit)
What causes this fault?
This fault occurs when the boiler detects that water is heating up far too quickly or that there is a significant temperature gap between the heat going out and coming back. It is physically caused by poor water flow through the unit, often due to a blockage, a failing pump, or a sensor that is no longer reading the temperature accurately. Essentially, the heat cannot be moved away from the burner fast enough, so the system pauses to prevent overheating.
This issue is more frequent in autumn when heating is first turned on after summer, as pump components can seize or sludge can settle during periods of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the displayBleed all radiators to remove trapped air that might be blocking water flow
Avoid the next call-out bill
A cover plan would handle faults like S.53: no call-out fees, no surprise bills.
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