S.4 Low
Your boiler is currently firing up to provide central heating and is functioning as expected.
Technical description: Heat mode – burner on error
Typical repair cost: £0 (including labour)
DIY fix possible
Check that your room thermostat is set to the desired temperatureEnsure your radiator valves are openMonitor the boiler to ensure it transitions to other codes once the heating demand is met
Protect yourself from future repair bills
A boiler cover plan would cover faults like S.4 — no call-out fees, no surprises.
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