Boilers Not Working

[Ric.ror]

Here's the problem
My mother thinks her boiler is not working - its a combi and the water is heating but the radiators are not coming on and the dial is not 'clicking' when she turns it.
Now I would have thought that its simply too warm for the thermostat to tell the radiators to warm up (apparently it did come on in the middle of the night on Friday). But the thing is my mother is 86 and terrified of A) being cold B) her heating not working.
Am I right or could there be another reason? I have looked on the website but the brochure on there is not very helpful at all.
BTW - its a Worcester - Greenstar 24i boiler

As always I am so grateful for any help

[Old_Geezer]

Ensure she has some fan heaters as back-up for peace of mind.

[CheekyChops]

Has she got one of those wall mounted thermostats and if so, can it be turned right down to see if the heating comes on then?

[Ric.ror]

Yes she does have a wall mounted one
Usually when she turns the heating up it gives a little click to register it's been activated but when she turns it around its not clicking at all
It's the fact her water is ok that's confusing as if it was the pressure the water wouldn't heat would it?

[The Builder]

The usual suspect is the 2-way valve in the boiler, stuck on Hot Water and not going over to direct the water to the Heating system.

That wouldn't stop the wall thermostat from clicking though. I would suspect a faulty WallStat first. Simple substitution, or even bypassing it would tell you for sure.