BoilerFaultCodesWhat the manual says
Manufacturer manualOverheat ’stat open/gas valve failure. Check wires/re-set ’stat. Test valve coils. Test for 230V and Neutral at PCB & plug on gas valve
What causes this fault?
This fault occurs when the boiler's internal temperature reaches a dangerously high level, triggering a safety switch to prevent damage. Alternatively, the boiler may have failed to detect the flow of gas required to maintain a flame, which is often caused by a failing gas valve or a communication error from the main control board. If the system cannot safely regulate heat or fuel, it shuts down entirely for your protection.
This fault is more frequent during the first cold snap of autumn, as components like the gas valve or pump can seize up after sitting idle throughout the summer months.
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 A04: no call-out fees, no surprise bills.
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