BoilerFaultCodesTechnical description
External temperature limiter has triggered (STB).
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, causing the safety switch to trip and shut everything down to prevent damage. The most common reasons are a failed pump that isn't moving hot water away from the heat exchanger quickly enough, or a blockage within the system pipework.
This fault is more common when the heating is first turned on after summer, as circulation pumps can seize up after long 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.
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