hot water but no ch on valiant vcw gb 242 eh. help

[frozensoul]

Just got back from hols last night. Turned on the heating and have been freezing since. Pump running and if I turn heating up to 28 on thermometer stat it runs for a while if I turn it of and on again at the mains.
Basically the bar on the expansion vessel is under 1 but if I get it to run long enough it goes upto just under 3 but drops quickly. however the temp read out on the expansion vessel never moves.

 

[bellairaphon]

So you have hotwater?

 

[bellairaphon]

Does the boiler fire when you turn the heating on?

 

[frozensoul]

Yep we've got water and no it doesn't fire up it makes the noises but no ignition. But if I turn it off at the mains for a few seconds then on again it ignites but cuts out just as the rads starts to warm up

 

[bellairaphon]

And when you run the hot does it stay lit constant.