It's a conventional vented system with two year old boiler, hot water tank and honeywell 3 port valve.
Last night I noticed that the rads were still hot, even though the heating timer on the Drayton LP522 control box (airing cupboard) had long since turned off. I found I could turn the boiler on and off using the wall thermostat, even with the heating set to OFF at the control box. We have hot water, and this morning with the rads cold, and wall stat turned down, I used hot water from tap, and the boiler hot water kicked in - so I think hot water is fine. With HW on, the control box HW button does turn the boiler on/off. I wondered about a frost stat operating, but AFAIA there is none.
Any ideas why the heating now appears not to be controlled by the CH/HW control box at all, and only by the wall stat? Where do you reckon the fault may be? What can I check?