F39 High
Your boiler has sensed it is getting too hot too quickly and has shut down to protect its internal parts from damage.
Technical description: Exchanger protection activation – possibly caused by no system circulation, air in the system or sensor damaged
Typical repair cost: £90-180 (including labour)
DIY fix possible
Check that your radiator valves are open and not turned to the off position.Ensure the boiler pressure is between 1.0 and 1.5 bar on the pressure gauge.Try bleeding your radiators to remove any trapped air that might be blocking water flow.
Protect yourself from future repair bills
A boiler cover plan would cover faults like F39 — no call-out fees, no surprises.
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Parts commonly replaced
- Temperature Sensor (NTC thermistor)
- Circulation Pump
- Main Heat Exchanger (if scaled)
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