grant combi problem

[wozza56]

Hi all ,im new here so be gentle
i have a Grant combi 90 mk 11 and it has all of a sudden stopped producing any hot water or heating . It will fire up if you turn the hot tap on but no hot water comes out and there is no heating at all ,one thing i did notice is a few times the vessel pressure drops to nothing and then a little while later will go up to about 2.5 bar even when it has only been filled to 1 bar ??
can anyone help point to what may be the problem

by the way its been in for about 4 years and apart from a problem from the factory which was sorted under warranty it has been fine oh and its oil fired
thanks in advance

 

[griggs]

When you say it fires up on DHW demand, but you get no hot water, how have you confirmed it is actually firing up?

 

[wozza56]

Right on closer inspection and after being told how much a new pump is i have come to the conclusion that it may just be a microswitch
the pipes into and out of the pump are hot and down to the diverter valve they are hot too and when the tap is turned on the plunger pops out of the diverter valve as i assume it should so the next things are the 2 microswitches which should be triggered by the diverter valve ,could it be these that are at fault ? and am i going in the right direction ?
thanks in advance

 

[oilhead]

The two microswitches fire the boiler and run the pump. Feel the pipework up to the blending valve. If it is hot from the heat exchanger to the valve, then you may have a faulty blending valve. Try adjusting it.