E21 High
Your boiler has detected an internal electronic signal failure and has shut down as a safety precaution.
Technical description: ADC lockout
Typical repair cost: £180-450 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like E21 — no call-out fees, no surprises.
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Parts commonly replaced
- Main Printed Circuit Board (PCB)
- Control Knob Potentiometer
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