FU High
Your boiler has detected that water is heating up too quickly or not circulating properly, which usually means something is blocking the flow of water through the system.
Technical description: Diff greater than 50c check isolation valves are open
Typical repair cost: £90-250 (including labour)
DIY fix possible
Check that all blue-handled isolation valves underneath the boiler are fully turned to the open positionEnsure all radiator valves (TRVs) are turned up to a high settingCheck your central heating filter for any obvious blockages if you have one installed
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
- Circulation pump
- Main heat exchanger
- Flow/Return thermistors
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