Help! Combi Boiler Losing Pressure

[cal76]

Hi all!

I'm new on here, and have very little knowledge of plumbing, so please bear with me...

I have a Sime Super 102 de luxe (combi) boiler which is losing pressure. Our plumber serviced it in April and discovered that the pressure was almost down to zero. He therefore repressurised the system (although he had to renew the stop tap on the flow pipe first in order to operate it). Anyway, he topped it back to 1.5 bar. Over the next few months I noticed it gradually falling and contacted him for advice. Although he suggested repressurising the system, I didn't feel confident about doing that myself so asked him to come out and do another service to check all was well and to repressurise it. Before he arrived I bled all the radiators, they had very little, if any air inside.

He checked everything and said it was fine, he also repressurised the system back to 1.5 bar. This was one and a half weeks ago (end of October). When the central heating isn't on the pressure is now just under 1 bar.

So now I'm worrying that the pressure will keep dropping and that something serious is wrong. I know how to repressurise in theory, but really don't like the idea of interfering with it, and have also read that it really shouldn't need repressurising as it is a sealed system. I've checked around each radiator and can't see any leaks. Plus, all of our radiators are hot all over, surely if there was a leak from the radiators or the pipes feeding them then the one at the top of the house would need bleeding? Wouldn't it?


Any advice about what could be the problem/how to diagnose it would be much appreciated!

Thanks

 

[ederz]

Expansion vessel or a leak on the system. Get him back out and check what pressure is in the expansion vessel as it might need pumping back up.

 

[willing2learn]

Might be worth getting someone else back that knows what they are doing (GSR'd of course). Sounds like a fairly straight forward issue.

 

[secret squirrel]

It is probably a very small leak that will take an age to find.

One of the things you can do is make sure all the connections from the rad valves to the copper tube is tight. If the engineer has checked the boiler over and can see nothing wrong you can assume that it is ok.

The next thing to is start isolating the system which is a pain to do as floor boards may have to come up, basically, you isolate part of the system and see if the pressure holds then isolate another part of the system eventually you slowly isolate the leak.

It may be a very small leak that dries very quickly and therefore never shows through a ceiling. If it is taking a few months to go to zero you may never find the problem as water loss is soooooo slow.

It is a pain in the backside for both you and your engineer, personally, I'd leave it alone. I would suggest leak sealer but I think you are not allowed to use this on combi boilers.

 

[cal76]

Thanks for your contributions. Secretsquirrel, the system was last repressurised a week and a half ago, since then the gauge has gone from 1.5 to just under 1 bar. Presumably if it carries on like that then the leak isn't that slow? If we were losing water via the radiator pipes or pipes under the floor that feed them then wouldn't there be a noticeable loss of warmth in the radiator at the top of the house? The pipework in our house is pretty innaccessible as we have panel, rather than floor boards!


So is it posible for there to be a leak within the boiler which doesn't actually affect the water levels in the radiators? And if that is the case, woudln't there be some outward indication if a leak?

Thanks again!

 

[DalesPlumbing]

Check the Pressure relief valve..

 

[cal76]

What's that?

 

[ederz]

The pipe that goes through the wall outside, It should be copper and be bent back facing the wall. Is it dripping?

 

[cal76]

I'll try and get out tomorrow and have a look, though it's a bit awkward to get to... I wonder how easy it will be to see if it's dripping? Especially if it's raining again tomorrow! Any helpful hints about the best way to check this also appreciated. Sorry, am clueless! Should get my fella onto it really, but he's even more clueless!