BoilerFaultCodesTechnical description
Primary thermistor (NTC) overtemperature
What causes this fault?
This fault occurs when the water within the boiler's main heat exchanger reaches an unsafe temperature, triggering a safety shutdown to prevent damage. The most common reasons are a pump failure preventing water from moving around the system or a build-up of sludge and debris that blocks the flow.
This issue often surfaces in autumn when the heating is first turned on after summer, as the circulation pump can become seized during 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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