S.20 High
Your boiler has detected an error while trying to heat your water, preventing the burner from lighting or staying on correctly.
Technical description: DHW mode – burner on error
Typical repair cost: £120-350 (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 S.20 — no call-out fees, no surprises.
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Parts commonly replaced
- Flow sensor
- Diverter valve
- Ignition lead
- Gas valve
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