BoilerFaultCodesYour boiler has sensed that the water returning to it is significantly hotter than the water going out, which usually means there is a blockage or a sensor error causing the system to stop for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Return temperature > flow temperature + 40 K (60 K for solar).
What causes this fault?
This fault occurs when the boiler detects that the water coming back from your radiators is much hotter than the water it just sent out, which shouldn't happen during normal operation. The most common reason is a lack of water flow caused by a blockage, trapped air, or a failing pump, but it can also be triggered if the electronic sensors that measure temperature become faulty and provide 'garbage' readings to the control board.
This fault is more common in autumn when heating systems are turned back on after a long summer break, as internal pump parts or radiator valves can seize up from disuse.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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