losing pressure on combi!! please help!

[novascotia]

Hi there
im having a problem with my combi. all was fine ie pressure constant at 1 bar for years. woke up this morning to find the combi wouldnt fire, and pressure was down to 0 . i reset the combi,filled the pressure back to 1 bar. i have checked all rad valves for leakage and all joints round the rads.
I have assumed that there is no leak from upstairs as the ceilings are not wet. I have had the floorboard up on 4 of the rads and can see no evidence of leak on any pipework there. The other rads i can get to under the floor as we have laminate flooring.
The pressure is still dropping slightly and has been topped up.
Im thinking of putting in some of that fernox leak sealer, is this a good idea or could it be something else.
anyone got any ideas please??/

 

[kevplumb]

check the prv outlet
the one that goes outside

 

[novascotia]

the presure never goes above 1.9 bar when the heating is on.
could the prv be the cause of a small pressure loss??

 

[kevplumb]

if its leaking

 

[novascotia]

just followed outlet from prv and its in the waste pipe from the sink. theres been a hole drilled and its just pushed in and siliconed in place. took it out of the hole and watched it for the last 5-10 mins and seen no water leaking from it.
i have now put some tissue under it to see if any water is coming out at all

 

[kevplumb]

not a condensing combi is it

 

[novascotia]

no mate a worcester bosch 240!!

 

[novascotia]

been checking prv for an hour now and no leaking is evident from it. could something be wrong with the expansion vessel?/

 

[kevplumb]

if the ex vessel was undercharged the prv is the first point of call
looks like the floors coming up

 

[novascotia]

think i might try some of that leak sealer , see if that cures the problem!!
does it work on small leaks which this one appears to be??

 

[kevplumb]

apparently

 

[DP]

So if I had a broken leg, I should take pain killers.

You have a leak. What magnitude? Have never liked these leak sealers and have never had to use one yet. What is the leak sealer plugs up a hole that needs to stay open to atmosphere?

If you are having to top up every hour or so, you will see wetness

If you top up the boiler every fortnight, leak will be minute. You will not have wetness but by looking for residues, it is possible to effect a cure.

Additional info would help

 

[weargas]

auto air vent on the 240 can leak within the combustion case without leaving poodles on the floor.

 

[StevieJB]

I've got a similar problem with my Vokera combi - everything was working fine (accept the banging CH pipes which kevplumb helped me out with...cheers!!) during the summer, but since the CH started on a timed setting it occasionally does not fire in the morning because of (apparently) not enough pressure. However when I add a tiny bit of water the pressure rockets up to 2 bar (from normal operating of 1-1.5 bar). I've got a Vokera engineer coming out on Friday, I'll let you know - he thinks its a dodgy pressure sensor (?).