BoilerFaultCodesWhat the manual says
Manufacturer manualExternal device fault (UHT/CPA)
What causes this fault?
This fault occurs when an external safety component, such as a condensate pump or an overheat thermostat, sends a signal to the boiler to shut down for safety. The most common reason is that the condensate pump has failed or is full of water, triggering a cut-off switch to prevent a leak or internal damage. It can also be caused by a loose wire or a fault in the safety sensor itself.
This fault is more common during the winter months, as frozen external drain pipes can cause the condensate pump to overflow and trigger the safety shutdown.
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 AL21: no call-out fees, no surprise bills.
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