ATAG Uncontrolled Heating / Valve Stuck Open

Radiators get hot even when the room thermostat is turned down or off

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Stuck diverter valve in heating position, Faulty external zone valve, Room thermostat or ATAG controller stuck calling for heat

Safety first: Isolate power before working on valves or controls.

Check the room thermostat or ATAG controller display to ensure it is not calling for heat; adjust settings or schedules.
Feel the flow pipe leaving the boiler when there should be no demand; if hot, the diverter or zone valve may be stuck open.
Gently tap the diverter or zone valve body to see if it releases.
Persistent uncontrolled heating requires replacement of the faulty valve or control by a technician.

Medium 3/5

ATAG diverter valve assembly

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