why does pressure drop overnight on ariston euro combi sx 20 mffice?

i have the same problem, if i pressure my system to about 1,5 and leave the heating on constant for a day or even a week its fine no problem even though the pressure jumps up to 3bar when on, as soon as i switch the system of the pressure drops to zero in about 20mins, i have changed the pressure valve thinking it was that but still the same problem, i asked a heating engineer he says it may be the exspansion tank behing the boiler may need pressure pumping up.
any ideas would stop the wife nagging

warren
February 2008

Bruce, Your boiler will only lose pressure if you have a leak somewhere on the system, sometimes the pressure relief valve can get a bit of grit stuck in the seal and this will cause the overflow to drip constantly and therefore cause the boiler to lose pressure overnight. You can try to clear it yourself by activating the valve two or three times to dislodge the obstruction, however it may need to be replaced which is not a very big job but may require a plumber.

CM
October 2006

Bruce, Sorry this isnt an answer so forgive me if i have got your hopes up!! I am having the exact same problem with my ariston boiler! Pressure dropping overnight and then it waking me up at 5 in the morning with a god awful screeching and banging sound. I have had 2 plumbers out to it, both have failed to fix the problem. I will keep trying and will let you know if i have any joy? Will you do the same?? Kind regards

Gemma Gregory
February 2006