BoilerFaultCodes.com
F6 Low Warning

Your boiler has lost communication with the sensor that measures the temperature outside, which helps it run more efficiently.

Monitor it

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 failure

What causes this fault?

This fault occurs when the boiler can no longer detect a signal from the small sensor located on the exterior of your home. The most common reason is that the sensor itself has developed a fault due to exposure to the elements, or the thin electrical wiring connecting it to the boiler has become damaged or loose. Because the boiler doesn't know how cold it is outside, it can't automatically adjust its settings to save you money on your heating bills.

This fault often comes to light during the first cold snap of autumn when the boiler attempts to communicate with the sensor to adjust for dropping temperatures.

Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Protect yourself from future repair bills

A boiler cover plan would cover faults like F6 — no call-out fees, no surprises.

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