BoilerFaultCodesWhat the manual says
Manufacturer manualMMI software incompatible with IRIS software Possible connection fault
What causes this fault?
This fault occurs when the water temperature inside the boiler exceeds a safe limit, triggering a safety sensor to cut the power. The most common reasons are a pump failure that prevents water from moving, or a blockage caused by internal sludge that traps heat within the main heat exchanger.
This fault often appears during the first cold spell of autumn when the heating is turned back on after months of inactivity, which can cause internal pumps to seize up.
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 F.20: no call-out fees, no surprise bills.
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