FU High
Your boiler has detected that heat is not moving away from the unit quickly enough, often because water flow is being blocked or restricted.
Technical description: Difference greater than 50c – check isolation valves are open
Typical repair cost: £100-£350 (including labour)
DIY fix possible
Check that the blue and red lever valves underneath the boiler are turned fully to the open positionEnsure all radiator valves (TRVs) are turned up to a high settingCheck your central heating filter (if fitted) to see if it is blocked or needs cleaning
Protect yourself from future repair bills
A boiler cover plan would cover faults like FU — no call-out fees, no surprises.
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Parts commonly replaced
- Pump
- Main Heat Exchanger
- Thermistor
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