Central heating operates when domestic only is selected

[matelot]

At the end of September I noticed that my central heating came on with only "domestic hot water" selected. It seemed to correct itself but has now reverted to the fault.
EG. With only domestic hot water selected the central heating rads heat up and the domestic "hot" water is cold.
I have a 5yr old "Calydra 100"Combi which has given no past prob;ems.
(UPDATE)
I have today switched off the boiled for 6hrs and now switched on to domestic hot water and all is working OK?
It seems that there is an intermittent fault with an electrically operated selector valve
Could any expert confirm this please?

 

[kablamar]

Need some more info please..... what type of clock/programmer do you have? What external controls are connected to this system. For example, is there a Y valve?

 

[Agile]

Need some more info please..... what type of clock/programmer do you have? What external controls are connected to this system. For example, is there a Y valve?

That seems unlikely with a combi boiler!

 

[kablamar]

What??? your saying there can be no external controls with a combi???

 

[Agile]

The word "unlikely" means that it is so uncommon that on any individual installation the chance is very low.

I can only think of two installations with a combi and external motorised valves! Probably 1 : 1000 against !

Tony

 

[kablamar]

The word "unlikely" means that it is so uncommon that on any individual installation the chance is very low.

but still very likely!

 

[namsag]

Why is it very likely

 

[kablamar]

As in not impossible, which is why i asked for more info before giving any advice.

 

[kablamar]

Why is it very likely

...and.....

 

[namsag]

Agile didn`t say it was impossible what he said was prob about 1 in a thousand would have additional external controls either for other zones or HW cylinder which is prob a good guess as they are few and far between so that would make it unlikely as opposed to very likely.
But yes your right there is nothing wrong with asking the OP this.

 

[kablamar]

 

[matelot]

That was interesting!!
No !all the controls are contained within the combi. Only a remote room stat controls the central heating which of course I can overide at the boiler

 

[Agile]

I see about 1 in 100 combis used as system boilers. Some of them have controls and cylinders. I did not include those in my 1 in 1000 figure as they are not being used as a combi.

My 1 in 1000 refered to a combi used to provide DHW and having a zone valve on heating or motor valve in asssociation with a cylinder. I can only think of three such installations! They are rare although a good way to use a combi.

I also see about 1 in 200 combis used as water heaters!

Tony

 

[matelot]

Does anyone know the answer to my problem?

Being an ex electrician I can deduct that the selector switch allows an EMF to flow thus creating a circuit, this to convert electrical energy int a mechanical force via (one assumes) a solenoid combined with a fluid valve. This valve (or valves) directs the hot water flow to either domestic hot water/with or without a rad feed/ rad only/ or OFF, depending on the selector switch position.

If we dismiss the selector switch then it must be the solenoid or the flow valve....As intermittent electrical faults are much rarer than mechnical, is it logical to assume that the problem lies with the flow valve? and will this be a combined or seperate flow valve/s?

 

[Agile]

Thats not a very useful attempt to immagine how a combi works!

Firstly they either are set for hot water or heating but NOT both at the same time.

I am not sure exactly which type of diverter valve yours has but I expect its moved by a small syncronous motor.

Hope that helps.

Tony