BoilerFaultCodesWhat the manual says
Manufacturer manualExchanger protection intervention
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the heat exchanger is getting too hot too quickly, which usually indicates that water isn't moving through the unit fast enough to carry the heat away. The most common reason is a failing internal pump or a build-up of sludge and debris that is restricting the flow of water through the system. In some cases, it can also be caused by air trapped in the heat exchanger or a faulty temperature sensor giving an incorrect reading.
This fault is more common during the first few cold spells of autumn or winter when the heating is turned on after a long summer break, as pumps can seize up during periods of inactivity.
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 F43: no call-out fees, no surprise bills.
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