BoilerFaultCodesWhat the manual says
Manufacturer manualDomestic Hot Water thermistor fault.
From this model's manual
Verified against the Glow Worm Xtramax He installation & service manual, page 33.
What causes this fault?
This fault occurs when the internal sensor responsible for monitoring your hot water temperature fails or sends an unreadable signal to the control board. The most common reason is that the sensor has suffered electrical failure due to age, or the wiring connecting it to the main system has become loose or damaged.
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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