Low
d.90 on Vaillant Home Combi

Your boiler is having a brief moment of confusion communicating with your wall-mounted thermostat, which is likely just a minor temporary glitch.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

StatusoftheeBUSroomthermostat

From this model's manual
Verified against the Vaillant Home Combi installation & service manual, page 33.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Check that your wall thermostat has fresh batteries and is switched on.Turn the boiler off at the fused spur for 60 seconds and then back on to reset the connection.Ensure the thermostat is within range of the boiler if it is a wireless model.

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Related fault codes

d.91View →d.92View →

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