i have a ferroli modena combi gas boiler. a couple of weeks ago the pressure dropped to 0.5 bar so the heating did not come on. i topped it back up to 1.0 then a few days later it dropped overnight again to 0.5 bar. this has been happening every few days ever since. we had a plumber out to check for leaks and he said there was no evidence of any leak. he also bled all the radiators incase it was air trapped in the system causing the problem but after a few days the pressure dropped again. i am hoping that because it takes a few days to drop that we do not have a leak!!

someone has suggested it could have something to do with the expansion vessel?? has anyone else had this problem or know how to fix it?? any help would be great

Gillian Corbett, February 2008

gillian.the pipes would tend to run round the walls rather than across the room and should be in a soft scree mis rather than the rock hard floor substrate even so a damp patch would be very noticeable cos the floor would have a damp proof membrane preventing any water to dissipate downwards. if the pipe work was not wrapped in syglass{greasy mucky bandage}
then the lime in the concrete will cause corosion and leaks especilly at joints where electrollisis will occur,if u do have to dig up the floor u may as well hav dun with it and do the lot , use plastic this time and avoid joints or fittings in the floor if poss.

colin r.j t., March 2008

if the water gets very hot its a temp control problem but the fitter should have spotted that.with my system it took 2 to 3 days after refill and bleeding and yes it was a leak all be it just a dripping from a pipe joint. use a screwdriver held to ear and listen to the pipes where they go into the rads,dont have the pump on and push the pressure right up to the limit and listen for the slightest of hiss if u hear something check all of the pipes and where it is loudest is the closest to the leak. nb if u got a small leak it will be on groumd floor or u would see it on the ceilings unless of course its running down youg cavity walls which may not notice for a year or so,

colin r.j t., March 2008

thanks Tony

the plumber suggested we could use a leak sealer but said that it can be risky and seal up the wrong hole and cause many more problems. Is this advice right? we are worried that the leak is under our downstairs floor which is concrete and would require the whole floor to be lifted to find the leak!

Gillian, February 2008

Hi Gillian

if problem is connected to the expansion vessel ,what will happen is when heating is on the presure gauge will raise to over 3 bar and release water/presure out of presure release valve then when heating is of it will go back down to .5 bar check to see if this is happening if not sure put a plastic bottle over the end of the discharge pipe outside and see if any water collects
If this is not the case then you do propably have a small leak somewere if you cannot find it add some fernox leak sealer to system which can be injected through the flling loop if you get the tube container type that fits into a silicon gun,this should seal any small leak such as yours

tony, February 2008