BoilerFaultCodesYour boiler has detected that the water coming back from your radiators is hotter than the water going out, which usually means the water isn't circulating correctly or a sensor is faulty.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like AL28 — no call-out fees, no surprises.
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