BoilerFaultCodesWhat the manual says
Manufacturer manualDIFF GREATER THAN 50°C - CHECK ISOLATION VALVES ARE OPEN, CHECK PUMP, CHECK RAD VALVES OPEN, CHECK SYSTEM BLOCKAGES
What causes this fault?
This fault occurs when the temperature difference between the water leaving the boiler and returning to it becomes dangerously high, usually because the water isn't moving through the system. The most common reasons are a failed internal pump that can't push the water around or a blockage in the system, such as closed radiator valves or a build-up of sludge. This causes the heat to stay trapped inside the boiler, triggering an emergency shutdown to prevent internal damage.
This fault is frequently seen at the start of autumn when heating systems are turned back on after a long summer break, as internal pump parts often 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 FU: no call-out fees, no surprise bills.
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