Boiler leak with no noticeable pressure drop

[matthussey]

In July we had our open vented back boiler break down so replaced it with a sealed condensing boiler. 2 radiators were replaced too but the remainder and pipes are the original ones.

Before the replacement we had air often collecting in our highest radiator, the bathroom towel rail. We were told this was most likely due to the pump sucking air in and collecting in the highest, and first, radiator in the system.

Our problem is that it seems to be still happening. The system is pressured to 1.5 bar and rises to a bit under 2 bar when heating. If I bleed the towel rail and pressure the system then over the next week the top rung gradually gets cooler but the boiler pressure doesn't seem to drop.

Over the summer I bled the towel rail regularly, despite not having the heating on, and got air out and the pressure dropped from about 1.3/1.4 bar that the system was originally pressured at to just above 1 bar. I am not certain but I believe that the pressure only went down when I bled.

I have tried bleeding the towel rail and then again about 6 hours later, without the heating having been on, and I get a small amount of air.

I pressured the system on Saturday morning while cold and I am avoiding bleeding to check whether the pressure does drop. So far it doesn't appear to have dropped. The rail is still warm but much cooler than it was on Saturday and cooler than the other rails. I can hold the middle of the top rail comfortably but I cannot touch the other rails, nor the edges of the rail for long.

I contacted the plumber and they said that if air is getting in then water is getting out and we must have a leak. They told us to go round all of the exposed pipework with coloured paper towels to see if I can find anything but I couldn't. Their response to me saying this was that it must be in the pipework but that it would be 'like looking for a needle in a haystack' to find. They recommended waiting for it to become more obvious.

I have spoken to other people who think it is an airlock or air getting released from the water that filled the system and will settle down. They say that the pressure would change on the boiler if it were leaking. They also question air getting into a pressurised system.

I'm not sure what to believe. I think it is probable that we have a small leak that we've had for a long time and now it's getting noticed.

Our piping is mostly within our first floor and it drops down to the radiators on the ground floor from the ceiling. I can only find one place where it goes through a wall.

I'm just not sure of what my next steps are to fix this. I've looked at getting hold of leak specialists to help but these aren't cheap. I could also contact my insurance but I'm not sure I really want to claim.

What should I be doing to fix the leak?

 

[gigz]

If the pressure is'nt dropping then you don't have a leak. Air will always rise to the top so if its the highest point thats normal. Did the installer flush and inhibit on install ? There is a possibility that its a hydrogen build up (google it). If it hasn't been in that long i wouldn't worry too much it could be that you have small pockets of air in the pipes/rads that will eventually work its way out.

 

[dilalio]

Stop worrying about the top bar of the towel rail and stop topping the system up. See how long it takes for the gauge to actually register a drop in pressure. My guess is that you have a very small leak which is 'flash' evaporating on exposed or hidden pipework so you'll never find it. If it persists then you could add a bottle of leak sealer to the system and see if that resolves the issue.
Otherwise: find that needle! Give all exposed valves and joints a thorough examination by wiping with a dry finger or blue paper and torchlight.

 

[matthussey]

He flushed and inhibited. I also tried lighting it and it's not hydrogen.

 

[matthussey]

Hi,
Since our third rail appeared to be taking longer to warm up I bled this morning.
Prior to bleeding the pressure was unchanged from 19 days ago at 1.5 bar. After bleeding it had dropped. In not able to read our gauge easily but it's around 0.1 or 0.2 bar. I have attached a before and after picture.
I captured the air in a plastic bag which I didn't light but the air didn't seem to rise like I would have expected hydrogen to. I thought this seemed like a safer test than setting fire to myself early in the morning.
Does this give you any idea of the size of our leak and what we would be able to do about it?
Thanks
Matthew

 

[gigz]

YOU DON'T HAVE A LEAK. It WILL drop when you bleed the water out, its supposed to.

 

[matthussey]

I didn't bleed any water out. I slowly bled and only got air. I only needed a small piece of tissue to wipe a single drop that came out when the air stopped.
The radiator rungs that had been cold before were now hot again.
I did not let any water out of the system. Just air that was in there somehow and was progressively making rungs colder. After a week one rung was cold, after two weeks two runs were cold, after the weeks the third was cold. Releasing the air made them hot again.

 

[dilalio]

If all your pipework is in the ceiling and the downstairs is on drops, then you would likely have noticed a leak by now. But, if you keep getting air out of the system (after several months) then a small leak would seem to be present! Make a mark on your gauge at the pressurised point and monitor it! Your gauge may be faulty also! If the gauge isn't dropping then the system is contained be it air/water/both!
If you want, try introducing a bottle of leak sealer and see what happens after that!

 

[gigz]

If your boiler pressure was holding for 19 days its unlikely you have a leak. When you let air out the pressure will drop (even if you don't bleed water out). When your heatings on the pressure will rise then go back to normal when it cools.

 

[Agile]

When bleeding hold a cigarette lighter under the vent and see if it lights if you want to see if it is hydrogen.

Go and find a good book and let your heating look after itself!

Tony

 

[snes]

Just an (unlikely) long shot - are all your rads steel? If not, then you could possibly have a chemical inhibitor reaction against an alloy rad.

As I said, very unlikely, but worth crossing off the list.