Low
d.09 on Heatline Monza

Your boiler is receiving an instruction from an external control device like a smart thermostat, and this code is simply confirming that it is operating based on those external settings.

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

Flow temperature set point from external eBus control

From this model's manual
Verified against the Heatline Monza installation & service manual, page 25.
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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