F39 Low
Your boiler's outside temperature sensor has developed a fault or disconnected, meaning the system may struggle to automatically adjust its heating levels based on the weather.
Technical description: Optional external probe error
Typical repair cost: £90-160 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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
- External weather compensation probe
- Wiring harness
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