This is really weird as I see the exact same question was asked before but the answer wasn't needed... I moved into a new flat last month heating atc been fine until today - I have no hot water and the boiler has started making a huge rumbling noise - there's no pressure in the water pressure gauge - where is the valve please? Is this dangerous?

Laura x, July 2007

Amatuer reply .Dont know a lot but have a excell 80E combi boiler and I have the installation and commissioning notes which say not to let the pressure fall into the red zone ( below pressure bar1 on the gauge! On those occasions when that started to happen I have opened briefly the "filling loop" tap to top up and closed that tap when back into the 'blue' zone above pressure'bar1'.
Filling loop is an added junction flexi pipe with tap and non return valve at respective ends connecting mains water to central heating pipeing, usually below the main boiler casing.In fact I have just had to have "loop" replaced because non return valve end was leaking (cost approx. £70-80).This also affects pressure.Another point is you should have a stop-cock valve on the mains pipe feeding water to your boiler, is it open?
Plenty of useful web.sites if you put in google the boiler name and type. regards brummie.- Hope it helps. PS. Quality C/H Boiler breakdown Insurance through D&G (reasonable cost) ,but if less than 8 years old usually.

'Brummie'(genuine), July 2007

you need to find the filling loop and top the boiler up to 1.5 bar

ian, July 2007

This is very unhealthy. You need to let water in till the guage reads 1 bar or so. There should be a typically white flexible plastic pipe going from the cold water main to the central heating pipe with a tap on the water main end, close to the tap that you use to throttle back the maximum hot water flow rate (to make sure that the water is still usefully hot with the bath tap full on).
If the pressure varies much when the central heating warms up then your expansion vessel needs recharging. This can cause your problem, high pressure with CH on (and over pressure valve lifting), no pressure with system cold.

c, July 2007