Heating only works when hot water working

[beardedbiker]

Why does heating always pack up when the weather gets cold?
We have been in this house for 5 years and the heating system has worked perfectly.
Now for some reason the boiler won't fire up to heat the radiators on their own but will only fire up when hot water requires heating. When this happens the radiators will heat up if the thermostat demands.
The pump appears to be working fine , the 3 port motorised valve appears to operate ok and I assumed that this meant the programmer was at fault. No such luck.
Just got a brand new programmer and fitted only to find I still have the same problem!!!!
Boiler is a Potterton oil-fired, programmer is Siemens/Landis, motorised valve is Landis, pump is Grundfos, tank stat is Landis and room stat is Landis.
I think the system is about 7 years old and as I say has worked perfectly up 'til now.
Can anyone help.
Would call a plumber but they are like hens teeth around here.

 

[chrishutt]

Why does heating always pack up when the weather gets cold?

Same reason cars always break down when they're being driven.

Problem is likely to be motorised valve and auxiliary switches therein. Loads of threads on this, so do a search.

 

[Pete.Cupra.R]

Yes......most likely motorised valve mate.
I had exactly the same prob a few years ago

 

[beardedbiker]

Thanks for the replIes guys. fitted new motorised valve and everything fired up as it should.
Then disaster. Everything was working fine,pipes were hot as were radiators and I was busy clearing up tools, mess etc. when I realised the pipes had gone cold. The boiler was making a noise but was not fired up.
I have now tried various combinations of switching on and off but without success. I have tried the reset button but that also has no effect.
Before you ask we have not run out of oil.I have checked.
Any bright ideas.
Cheers

 

[chrishutt]

Are you sure you wired up the motorised valve correctly? The wiring of a 3 port mid-position valve has a peculiar wiring arrangement which it's easy to get wrong.

 

[beardedbiker]

Was very careful to wire up valve exactly as old one, taking out one wire and replacing with the other.
Also it did definitely work for a while.