What's wrong with the feed to my towel rails?

[Talkingbollox]

I have separate upstairs and downstairs circuits, and the towel rails came on indpendently of the upstairs radiators. Just recently the towel rails would only come on when I call for heat by adjusting the upstairs thermostat.

Any ideas please? Is it a valve somewhere?

Thanks in advance.

My airing cupboard looks like this:

 

[mickyg]

assuming the feed to the towel rads is the one far left in 15mm. Whenever there is a demand on the system they will come on. Whether it be hot water or either of the ch demands. Are you using your immersion for hw at the moment by any chance?

 

[Talkingbollox]

Thanks for the quick response.

Whenever there is a demand on the system they will come on.

Yes, that used to be the case.

Are you using your immersion for hw at the moment by any chance?

No, I'm not. HW and GCH on at the programmer, same as before.

The only thing I have changed recently is the programmer (another faulty Sunvic 207XL - the fourth in less than 3 years).

Any ideas?

 

[Talkingbollox]

I managed to fix it by turning up the cylinder stat. It was set at 45 deg C.