Combi boiler query

[Welsh_sparky_21]

So I’ve been having this issue with my boiler for a while now, I’ve currently got one stat in the hall that when I turn it on it brings the heating on. Very basic, it’s low voltage switching. See when I turn the heating off it takes ages to go off, it’ll heat the radiators up to absolutely boiling temperatures and it’ll also turn itself on when we are out and the house is absolutely roasting hot when we come in. Now a tried fitting a new stat and the same thing happens so I know it’s not an issue with that not isolating it, any ideas?

 

[littlespark]

There is usually one or more motorised valves in these systems. Silver box on the pipework.

What’s happens is, the stat controls the valve, and when that is fully open, it closes an embedded micro switch that then turns on other things…
This switch may be sticking on.

The valves usually have a manual override lever which you can move over if the valve is closed. (But not the other way)

 

[Welsh_sparky_21]

There is usually one or more motorised valves in these systems. Silver box on the pipework.

What’s happens is, the stat controls the valve, and when that is fully open, it closes an embedded micro switch that then turns on other things…
This switch may be sticking on.

The valves usually have a manual override lever which you can move over if the valve is closed. (But not the other way)

yeah that makes sense, thanks mate

 

[Mike Johnson]

The lever on the side of the metal case will not have any resistance to movement when the valve is open, but will have resistance when the demand is not there, one thing that happened recently on an instillation was the rubber ball closing valve inside the unit was being by-passed due to age, not seating properly, easy to tell if the pipe one side of the valve is hot and the other side is cold, then its working, but if both sides are hot and the demand is not there for that valve, (hot water or CH) then the valve is being by-passed.

 

[freddo]

Combi boilers don't normally have zone valves.

What is the model of boiler?