BoilerFaultCodesYour boiler has lost communication with its external controls or is stuck in an internal testing phase, meaning it cannot start the heating cycle.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temporary fault code (Refer to section 7.10)
What causes this fault?
This fault occurs when the boiler's main control board loses the electronic signal from the external timer or room thermostat, causing a break in communication. It can also happen if the boiler becomes stuck in an internal calibration mode after a power cut or a system reset. Essentially, the 'brain' of the boiler is waiting for a command to start that it can no longer hear.
DIY fix possible
Locate the selector switch on the front panelTurn the dial to the 'OFF/RESET' position and wait for 10 secondsTurn the dial back to the 'Hot Water' or 'Heating and Hot Water' position
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like 21 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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