Gas boiler pressure drops, is this culprit?

Hey,

I've read previous posts here about gas boiler systems dropping in pressure on a daily basis. It could be a leak, as well as a faulty pressure valve at the boiler, from what I understand.

My boiler shows that the pressure can drop from 3 bars after topping up the system, back down to 1 bar. Another day later, and the pressure is now below 0.5. I had the boiler checked 2 days ago, and they guy said to see if the pressure drops every day (which it does).

So I looked around quickly, and the image below is of a downstairs radiator valve that had a drop of water on it. Could this be where the water is leaking and evaporating?

I'm posting a picture, because I'm not sure what that horizontal pipe is supposed to be doing. Any enlightenment? Could it indicate that the previous owners were having problems?

I just moved in last week.

I have the same problem. I dont know where the water is going. Stick a little bit of tissue in the boiler overflow drain pipe on the outside wall to see if its dripping.
I'm told that topping up with fresh water is bad for central heating pipes.

Re the picture - yes green mould on copper indicates there was a leak at some point over time.

Thanks, I'll test the overflow pipe.

you could try tighting the silver nuts a half turn and see does this stop the leak, also clean up around the pipe with a wire brush to see if you can see where the leak is. also when the boiler has been running for a while and the system is realy hot look outside the house where the pressure valve outlet pipe comes through the wall (usally near the flu),and see if theres steam or water comming from the pipe, in my case the valve was only leaking when the system was really hot and what was leaking was evaparating straight away,

And if it turns out that the outside pipe is leaking, what's the solution? Call Bord Gáis, or a plumber?

if you are handy in these matters you could depresurise the system and replace the valve and then represurise the system and bleed the rads otherwise leave it to a local plumber!

Ur system water presure should be between 1-1.5bar when system is totally cold
If u fill it to 3bar then the pressure safety cable will lift (and more than likely drip forever until changed)

When boiler is on does pressure when correctly set as above rise to 3bar or over (again cable will release water at this pressure) if so, the expansion vessel has lost it's charge, may have a leaking air valve or have perished.
Your service guy should have checked this for you

If those are all ok and your system is still losing pressure then yes you have a leak somewhere

As for toiletpaper to test. Serviceman should isolate and drain the boiler. Then remove the valve a blow through it to see if it's good or bad (only takes a few mind)

Your system pressure should never be any where near 3 bar.

If your system is dropping that fast it is unlikley to be a weeping rad valve.

oops. All above red to 'cable' should be valve. Strange spellcheck!

@DGOBS The pressure was at zero when I moved in. Called the service man, he said to keep it around 1 to 1.5. But while showing me how to up the pressure, he got it up to 3 bar.

The red pressure pointer that never moves is set to 1.5. Does this mean that the system releases water if the pressure gets above this red point?

After two days of using the heating for a couple of hours each day, the pressure had dropped down to 0.4 when the system had fully cooled.

I have topped it off to 1.5 again. I have just tightened the suspicious radiator valve too, the bolt didn't feel like it was very tight.

(BTW, can anyone tell me what that valve-type contraption on the radiator pipe in the picture is?)

The red arm is only a marker and does nothing. The PRV is preset to release at 3 Bar.

Keep an eye on the termination outlet of the pressure relief valve (normally outside) to see if it is letting by. It may be hard to spot if it is doing it slowly and irregularly.


As DGOBS has stated, your expansion vessel may need to be charged or replaced. You may have a leak on your system.

The valve you refer to is a drain off cock (DOC). You attach a hose to it and drain down system when needed.

I checked the tissue in the outside pipe, it was definitely wet, so I presume that's how the pressure is dropping. So I guess I have to call a plumber in to check the pressure release valve.

get a good serviceman and he will replace the prv and give ur appliance a proper service to (and system check if ur lucky)

Where r u based?
I may be able the recommend someone

So, a certified gas serviceman, rather than a standard plumber is what I need, right?

The guy who came out last week was associated with Bord Gáis.

I'm in Limerick city. Would appreciate a recommendation if you have.