L1 High
Your boiler has shut down because the water inside it has become too hot, likely due to a circulation problem.
Technical description: Flow temperature overheat
Typical repair cost: £120-£350 (including labour)
DIY fix possible
Check that your radiator valves are fully open to allow water to flow.Ensure your system pressure is between 1.0 and 1.5 bar on the pressure gauge.Press the 'Reset' button on the boiler control panel once the unit has cooled down.
Protect yourself from future repair bills
A boiler cover plan would cover faults like L1 — no call-out fees, no surprises.
*Affiliate links — we may earn a commission at no extra cost to you. Prices shown are starting prices.
Parts commonly replaced
- Circulation pump
- Overheat thermostat
- Thermistor (NTC sensor)
*Affiliate links — we may earn a commission at no extra cost to you.