BoilerFaultCodesYour boiler is having trouble reading the outside temperature and is unable to adjust your heating efficiently.
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: Outside sensor S5 defective
What causes this fault?
This fault occurs when the boiler loses communication with the sensor installed on your outside wall, which usually means the sensor has developed an internal electrical fault. It is often caused by moisture getting into the sensor housing or a break in the thin wiring that connects the sensor to your boiler. Without this data, the boiler cannot automatically adjust its temperature based on the weather outside.
This fault is more common during autumn and winter when heavy rain and frost can cause corrosion or moisture ingress within the external sensor unit.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like E27 — no call-out fees, no surprises.
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