more boiler help please

one main thermostat on wall? if so, where?

in the hall.

but when the boiler cuts out there's still a fair way to go before it "clicks". if you know what i mean.

Could be an airlock,what type of boiler and how old?

my guess is the pump is stuck/not circulating properly.
Boiler is cutting out on overheat stat. NAP

I had a new boiler installed last Febuary.Around about the beginning of December,before it got really cold, it developed a fault.Coming on from cold in the morning it would run for about 35-40.Thereafter,it would keep cutting in and out as it cooled.The thermister was faulty.Does this 'ring any bells'?

Now that it's really cold outside,the boiler is unable to cope with the demands being placed upon it and we are currently unable to achieve the requested temperature.Guess it's just not powerful enough for the size of our house or we need more radiators,which get too hot to touch for more than a second.The thing is,the boiler can only heat the circulating water so much and then it will turn itself off.This appears to be what's happening with mine.

You need to speak to the person who installed your boiler Jambo.
If that is true, your boiler is undersized, but my guess, is that the old system wasn't properly flushed.

Oxford,Are you knowledgable about these matters.The boiler is an Ideal Icos HE 24.It's in an ex -airing cupboard on the upper floor, so there were space constraints.We have a 4 bedroom semi.The upper floor rads heat up quickly,but one of the downstairs ones is slow to warm.Does this fit with your flushing theory ?

It's my living :)
24 KW boiler should comfortably heat 12 or more radiators. More inclined to think yours, as is original posters prob, is a circulation prob.
Blockage, stuck pump ?
Try turning valves off to all rads that get hot and see if one/ones that don't get hot, do start to get hot.