BoilerFaultCodesYour boiler has detected an internal electronic signal failure and has shut down as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: ADC lockout
What causes this fault?
This fault occurs when the boiler's internal computer can no longer accurately read or process the electronic signals from the control dials. It is typically caused by a failure in the main circuit board's circuitry or a broken connection in the knobs you use to adjust the heating. Because the boiler cannot confirm your temperature settings, it shuts down to prevent unpredictable behavior.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like E21 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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