BoilerFaultCodesWhat the manual says
Manufacturer manualCentral heating return sensor overheating
What causes this fault?
This fault occurs when the water traveling back into the boiler from your radiators becomes excessively hot, causing the system to shut down to prevent internal damage. The most common reason is a lack of water circulation, often caused by a failing pump or a buildup of sludge and debris that blocks the main heat exchanger.
This fault is more common when the heating is first turned on after summer, as circulation pumps can seize up 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 21E: no call-out fees, no surprise bills.
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