BoilerFaultCodesTechnical description
Internal control box error (high limit circuit fault)
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the water temperature has exceeded safe limits or if the main control board has suffered an electrical failure. It is often caused by a lack of water circulation, such as a failing pump or a blockage in the heat exchanger, which prevents heat from being carried away from the unit. In some cases, the error is triggered by a communication fault within the boiler's electronic 'brain' itself.
This issue is more frequent in winter when the system is under high demand and any underlying circulation issues or pump fatigue are pushed to their limit.
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.