BoilerFaultCodesYour 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.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Optional external probe error
What causes this fault?
This fault occurs when the boiler loses communication with the sensor located on the outside of your property. The most common reason is that the sensor's internal components have corroded due to weather exposure, or the thin electrical wires connecting it to the boiler have snapped or come loose.
This fault is more common following periods of heavy rain or extreme frost, which can cause moisture ingress or wire damage in the external sensor housing.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like F39 — no call-out fees, no surprises.
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