BoilerFaultCodesYour boiler has lost communication with the safety sensor that prevents your underfloor heating system from getting too hot.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: External under floor heating thermostat defective.
What causes this fault?
This fault occurs when the link between the boiler and the safety sensor protecting your underfloor heating pipes is broken. The most common reason is a hardware failure in the external limit thermostat or a loose connection in the wiring that prevents the boiler from confirming the floor temperature is safe.
This fault is more common in autumn and winter when the underfloor heating is first switched on after being dormant for several months.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like A6 — no call-out fees, no surprises.
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