BoilerFaultCodesWhat the manual says
Manufacturer manualALTERNATING 'H9' GO TO FRAME 93
What causes this fault?
This fault occurs when the water temperature inside your boiler rises too quickly or exceeds a safe limit, causing a safety sensor to trip. The most common reasons are a failed pump that isn't circulating the water properly or a blockage in the pipework that is restricting flow. In some cases, it can also be triggered by air trapped inside the system or a build-up of limescale in the heat exchanger.
This fault is more common in autumn when heating systems are switched back on after being idle all summer, which can cause internal pump parts to seize.
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 H9: no call-out fees, no surprise bills.
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