Medium
F90 on Heatline Sargon 30

Your boiler has lost its connection to the external temperature sensor or the central heating thermostat, meaning it doesn't know when to turn the heating on or off.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

CH thermostat

Referenced from a related model
This code was carried over from a closely related model. Treat it as a guide and confirm against your boiler’s own manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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Related fault codes

F10View →F11View →

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