Boiler losing pressure when off but holds when on?

[v1dl3r]

So my combi boiler is losing pressure. Has been for a little while and I have been naughty and been topping it up. I'm no stranger to DIY but know very little about the art of plumbing and even less about central heating - I can change a radiator but that's about it! Finally called an engineer out who charged me £300 to not fix the problem so have decided to try and get to the bottom of the issue myself!

The boiler losses pressure, about 1bar every 8-10 hours. When I isolate the boiler from the central heating system I get no drop is pressure. This leads me to be believe that there must be a leak somewhere in the central heating pipework. There is no weeping from the radiators and no visible signs from the floor which after a few months of topping up I would have expected to see, it's a screed floor which the pipes run though and has floorboard on top (??). What is throwing me is when I run the boiler with the central heating system attached I get no drop in pressure! I ran it on the lowest setting for a whole day and no pressure was lost. This would lead me to believe that perhaps it's not under the floor.... I'm really starting to scratch my head about this one.

Was wondering if anyone else had experienced the same sort of problem or could point me the right direction. Any help is much appreciated.

Thank you in advance!

 

[Alex Beckett]

Hi,

Do you have a filter or any thumb/auto air vents (bleed) vents visible on the system as these could be leaking? Also when the system is running or hot the natural expansion may be covering up the leak if it is from a rad valve or similar, although if its loosing 1 bar in 8 hours then im sure you would have seen some staining/wet patches on the floor under rad. Other than that maybe under the floor and just not showing through.

 

[Gray0689]

Unfortunately we are not allowed to give you info on this
As its a gas boiler and you would have to take cover off to investigate

But if you put up your area I'm sure there would be someone decent near you to come and fix it
Could be quite Simple from your description

 

[gassafe]

1 bar every 8 hours is a lot of water!
You said you paid £300 pounds to a plumber who did not fix it, for that sort of money he should have done a lot of remedial work in tracing down the fault, what did he do or change?

 

[gassafe]

Where does the condensate from the boiler go to / terminate!? It could be leaking there if the heat exchanger has failed.

 

[Gray0689]

Gas safe Job 38-11 is coming soon lol

 

[Dotty]

Not the boiler chaps, read the second paragraph.

 

[Gray0689]

Not the boiler chaps, read the second paragraph.

Never read that bit lol

Yes you have a leak in heating system
Try some leak sealer in it

 

[gassafe]

Possibly a leak in the screed, a leak upstairs would show with a damp ceiling already!

You could try leak sealer but with a drop that big it probably won't last long! You may have to find the leak or repipe the radiators from pipework drops to each rad!

 

[Gray0689]

Miracle SealMiracle Seal Permanently seals small leaks anywhere in the cooling system. Seals leaks in radiators, hose pipes and water pumps.
CT1 stuff looks good but as of yet I haven't tried it

Let us know if it works for you

 

[v1dl3r]

Thank you everyone for your responses! I wasn't expecting so many.

Hi,

Also when the system is running or hot the natural expansion may be covering up the leak if it is from a rad valve or similar

That's an interesting thought. Although I have ran the system at 40degrees which I wouldn't have though that would have been enough heat to expand the pipe and plug the gap.

I have bought some of the CT1 stuff from the interwebs, are any of you lovely folk in the West London area? If so would you quote me coming and flushing it through the system for me?

Thanks in advance.

 

[gassafe]

How many did you purchase, it looks like 1 does 25 litres, so a 100 litre (10 rad system roughly) would require 4!!

The leak is most likely in the downstairs screed fed rads so you would be better off shutting off all the upstairs rads & letting the full dose circulate round the downstairs radiators, you could then open up the upstairs rads and send it round the full system!

 

[v1dl3r]

it's only a small flat with 5 rads. Actually two of the rads do go under some crawl space, one of the rooms is part of the original house, the rest is an extension. My money is that the leak is in the crawl space as its the only place where it wouldn't have shown straight away. The whole floor through the entire flat is one piece oak floor boarding so don't want to start ripping it up.

If i'm confident that the leak is not in the rads can i turn them off and just pump it through the pipework? Or is that not how the rad's work?

 

[Gray0689]

No put it through the Rads too to get circulation through everything

 

[Gray0689]

Masood is in London I think