BoilerFaultCodesWhat the manual says
Manufacturer manualTemperature differential inverted (return sensor temperature higher than flowsensor temperature)
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water returning from your radiators is hotter than the water being sent out, which is physically impossible during normal operation. The most common reasons are a pump failure preventing water from moving through the system, a blockage in the heat exchanger, or a sensor that has become unclipped or faulty.
This issue often surfaces in Autumn when heating systems are turned on for the first time after summer, as pump components can seize during long periods 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.
Avoid the next call-out bill
A cover plan would handle faults like AL28: no call-out fees, no surprise bills.
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