Medium
D.24 on Vaillant Turbomax Plus 828

Your boiler is struggling to operate because external controls like your thermostat or timer are sending conflicting signals or aren't communicating correctly with the main unit.

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

Diagnostic code check (page 52) / External controls check

From this model's manual
Verified against the Vaillant Turbomax Plus 824 828e installation & service manual.
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 room thermostat is turned up higher than the current room temperature.Replace the batteries in your wireless wall thermostat or programmer.Ensure your external timer or smart hub is switched on and has a stable connection.

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