L1 High
Your boiler has shut down because it thinks the water inside is getting too hot or is not moving through the system properly.
Technical description: Flow temperature overheat lockout or no water flow lockout
Typical repair cost: £100-350 (including labour)
DIY fix possible
Check that your radiator valves and any isolation valves are fully openEnsure your system pressure is topped up to between 1 and 1.5 barBleed your radiators to remove any trapped air and then reset the boiler
Protect yourself from future repair bills
A boiler cover plan would cover faults like L1 — no call-out fees, no surprises.
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Parts commonly replaced
- Circulating Pump
- Thermistor (NTC Sensor)
- Main Heat Exchanger (if blocked)
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