Boiler set to HW only but upstairs rads still coming on

Hi there,
First post etc...
Hope someone can kindly advise.
We have a recently installed (14months ago) closed loop CH/HW system. Over the weekend we noticed that although the room thermostat was set so the rads wouldn't heat the upstairs ones were still warm.
Last night we actually turned the boiler to HW but the same thing is still happening, downstairs rads cold, upstairs warm.
At work at the moment so sketchy on the specifics of the system.
Thanks in advance
Flimtoe

have you a valve like this



if the hw only on feel all three pipes to the valve are they all hot ?
or you may be getting reverse circulation.

Thanks!
Yes all three pipes are warm.
I know that our one of those is a Honeywell and the slider/switcher is underneath, should that be in a particular position?
Is reverse circulation bad news?

reverse circulation is not good.

but if your only on hw and the pipe from the valve to the rads is same temp as the hw side to cylinder then the valve seem to be passing to heating when it should be closed.

does the pipe still freel the same temp as far as you can feel it from the valve ?
it will be warm near the valve cause of heat transfer.