Sunvic TLX thermostat or boiler the problem?

[Cath99]

I have a Sunvic TLX thermostat - this one, I believe:

http://www.uk-plumbing.com/sunvic-r...5.html?zenid=c9e346cf7cfee920947e2eba941f0dfc

The problem I'm having is that when it is set to 20 degrees and the hall, where it's located, is certainly colder than that (I have a thermometer to check), the boiler doesn't come on. It will only come on when I turn up the thermostat to a much higher temp - often 24 or so. I can then turn it down and it will often stay on, though sometimes it clicks off again. But the thermostat seems to register the temperature, i.e. it 'clicks' when it reaches the room temp. But the boiler won't come on as a result of this if the thermometer is turned higher than this.

So, my question is: is it the thermostat that needs replacing (certainly a possibility as it looks old) or is there something up with the boiler? Boiler is a Saunier Duval.

Many thanks

 

[seco services]

sounds like it times for a new stat.

 

[kevplumb]

Reliable temperature control via built-in Accelerator Heater

from the spec


but is it connected

 

[Cath99]

kevplumb: thanks - I would assume so as the thermostat has worked reliably for some time and has only recently started playing up.

Any other thoughts or is the consensus that it's the thermostat that needs replacing?