BoilerFaultCodesTechnical description
Safety Thermostat Activated (Boiler or Flue)
What causes this fault?
This fault occurs when the boiler's internal temperature exceeds safe limits, triggering a safety sensor to cut off the gas supply. The most common reasons are a failed pump stopping water from circulating or a build-up of limescale and sludge creating a blockage that traps heat inside the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after months of inactivity, as pumps can seize during the summer.
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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