BoilerFaultCodesYour boiler is having trouble communicating with an external control accessory, meaning some remote settings or external commands might not be working as expected.
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: No external operating mode changeover via external extension
What causes this fault?
This fault occurs when the boiler loses its physical connection to an external accessory, such as a plug-in extension module or a third-party controller. It is usually caused by a loose communication wire or a hardware failure within the interface module that handles external commands. While the boiler typically continues to heat, it can no longer receive specific instructions to change its operating mode from these outside devices.
DIY fix possible
Locate your boiler's power switch and turn it off for 30 seconds, then turn it back on to reset the communication.Check if any external smart home controllers or extensions are unplugged or have lost power.Confirm that your thermostat or external control unit is displaying information and has fresh batteries if applicable.
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A boiler cover plan would cover faults like 91:0 — no call-out fees, no surprises.
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