Hot water demand fires boiler when controller turned off

[BlessedlyBrian]

Hi. We have an issue that when the system controller is off, the boiler is still firing up and heating the hot water. Boiler is a Grant vortex Eco external 26-35. Controller is a danfoss with wireless thermostat. Grunfoss pump. All is about two years old. We had the plumber out recently and he replaced the motorised valve and you can hear that working fine. There is nothing only one valve. Whole system appears off but the boiler still fires up and the overflow rad in the bathroom is still hot, none other of the other rads are hot.

Has anyone any ideas on what might be causing this?

If you need any more info please just ask.

Thanks
Brian

 

[simond]

Hot water zone valve jammed open

 

[BlessedlyBrian]

Hi Simon. I can only find one valve and that was replaced a few months ago. Would there be another

somewhere?