High Lockout
DHW pump on Grant Vortex Pro Combi 26

Your boiler is struggling to manage the temperature of its internal hot water store, meaning you likely have no hot water available.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

If flashing this indicates either a store thermistor or PCB fault

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that monitors the temperature of your stored hot water. The most common reason is that the sensor has developed an electrical fault or the wiring has vibrated loose, preventing the boiler from knowing when to safely heat the water. In rarer cases, the main control board itself may be failing to process the signals it receives.

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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