Pressure dropping in sealed central heating system

[boilerwoes]

I am not having a good time with our central heating system! (See other threads for issues with working gas pressure at boiler, but that's another story).

Currently the water pressure in our combi central heating system (Vaillant ecotec plus 831) is dropping at the rate of about 0.1 bar a day. it has 11 rads, and for the life of me, I can't identify where it is leaking. I have isolated the boiler from the system for a week and it is clear that the issue is not with the boiler. I have done some of standard checks of looking at TRVs etc but, nothing noticeable.

The expansion vessel has a pressure of about 0.8 bar. Water pressure in boiler originally at about 1.2 bar.

So - I have a number of questions:

1. [*=1]How much water is being lost to drop the pressure at 0.1 bar a day[*=1]Is this leak a "major issue" and does it need to be resolved, or shall I just live with topping up pressure once a week, given this leak is not visible or causing visible damage to the house?[*=1]If I do add a dose of leak sealant, is one enough for this size central heating system?[*=1]What is the best leak sealant to use...

Regards!

 

[dontknowitall]

Has the expansion vessel been checked?

In case you don't know, if it's a gas boiler it's illegal for anyone to work (or even check/diagnose) on one unless they're Gas Safe registered.

 

[iltryhelp]

Its not a major leak by the sounds of it however you cant keep just topping it up every so often as you will eventually rid the system of inhibitor. Have you checked outside the property for a dripping blow off pipe? Ive found it quite common that a bit of grit etc can get stuck in the rubber seal of the blow of valve and hense wont allow it to seal properly again once its been used.
I guess you could try leak sealant but i wouldnt know as i never use the stuff. Although i would think .1 bar a day might be a little to much for a leak sealer to work, generally they are good for 'sweats'

You say you cant find the leak anywhere? have you checked everywhere? i mean its possible that its coming from a solder/comp fitting anywhere (underfloor etc) that you may have overlooked.

 

[boilerwoes]

Has the expansion vessel been checked?

In case you don't know, if it's a gas boiler it's illegal for anyone to work (or even check/diagnose) on one unless they're Gas Safe registered.

Hi - absolutely, however, it is legal to top up.

The reason I know the expansion vessel is at 0.8bar is because the Vaillant engineer (who came because the boiler is under warranty) pumped it up. He couldn't see any leaks in the boiler or the overflow and he seemed to think the expansion vessel was fine (this is the one that is pumped up with a bicyle pump, right?). The boiler is about 3 years old now (just under).

 

[iltryhelp]

0.8 bar seems to low for an expansion vessel to me, although im not sure about these boilers.

 

[boilerwoes]

Its not a major leak by the sounds of it however you cant keep just topping it up every so often as you will eventually rid the system of inhibitor. Have you checked outside the property for a dripping blow off pipe? Ive found it quite common that a bit of grit etc can get stuck in the rubber seal of the blow of valve and hense wont allow it to seal properly again once its been used.
I guess you could try leak sealant but i wouldnt know as i never use the stuff. Although i would think .1 bar a day might be a little to much for a leak sealer to work, generally they are good for 'sweats'

You say you cant find the leak anywhere? have you checked everywhere? i mean its possible that its coming from a solder/comp fitting anywhere (underfloor etc) that you may have overlooked.

As far as I am aware, the Vaillant engineer looked at that and seemed to think the PRV wasn't the issue. I did leave a plastic milk bottle attached to the blow off pipe to capture water and it didn't really catch anything. I will try again when it isn't raining to see!

In terms of looking for a leak - well, I have looked everywhere that is visible, and accessible - not done under floors. We have laminate flooring downstairs, and given that we haven't seen any signs of the leak, I suspect it might be downstairs as it would simply drip underneat the floor and not be visible at all. It feels like overkill to rip up laminate flooring to check down there, so will do that at the last resort.

My other options could be to see whether my insurance company covers this sort of thing and get them to do it on that? Anyone had experience of leak detection companies? Are they likely to find a leak of 0.1bar a day? Feels like that might be the least invasive approach if the insurance company will pay...

 

[boilerwoes]

0.8 bar seems to low for an expansion vessel to me, although im not sure about these boilers.

Just checked the Vaillant manual online - pressure should be 0.75 bar, so I think it should be ok?[http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf]

 

[RoryD]

the heat exchanger is more than likely leaking and discharging down the condensate. If the engineer turns power off to the boiler, diconnects the condensate and tops the pressure up - maybe until it's a bit too high - then if there is water coming out of the condensate the heat exchanger is leaking and a replacement is required. If you're under warranty or if you've only recently called out the vaillant guy, get him back lively

 

[AWheating]

if its not at the boiler and not visable above floor then is probably a micro leak under your flooring, best to get it found and fixed before it get worse or damages anything.

 

[Ian10261]

If it turns out to be leaking under the floor, and you've got solid floors then consider re-piping all the downstairs rads from above. Its a fairly big job but worth it in my opinion.
Copper pipes burried in screed without any protection will give up the ghost sooner or later due to the corrosive effects of the cement. Its all very well finding the leak and repairing it but there no telling that its not going to happen again somewhere else.