BoilerFaultCodesTechnical description
Flue sensor fault or burner output modulates to maintain temperature set (potential heat exchanger obstruction)
What causes this fault?
This fault occurs when the boiler's internal components reach a temperature that is dangerously high, triggering a safety shutdown to prevent damage. The most common reason is a buildup of limescale or debris inside the heat exchanger, which restricts water flow and prevents heat from being transferred away from the burner effectively.
This fault often becomes apparent during the first cold snap of winter when the boiler is suddenly required to run at a higher output for longer periods.
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.
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