Pressure Increasing

[galwegian]

I have a 5 year old Ideal Classic Gas Boiler on a sealed system which has been running fine until I decided to get involved (boy, do I regret that now). The pressure had dropped to just below 1 bar so I decided to increase it using the Filling Loop, which seemed to work fine…I increased to 1.5 bar.

However, once I turned the boiler on it continued increasing to 3.5 bar, at which point I used the PRV to reduce it to 1.5 bar again. I turned off the boiler but it still increased to 3 bar over the next 4 – 5 hours. I keep reducing the pressure using the PRV but it gradually increases again, increasing faster if the boiler is on. At one point I reduced the pressure to zero bar by bleeding a rad in the kitchen, when I turned the key the water sprayed out about 5 feet and did not decrease in force that much even when it had reached zero.

Strangely, the Filling Loop is permanently attached to the system, I should probably change this to a detachable loop. I know the wheel is closed tight but it’s always possible that there is a leak into the system. How likely is this and what is the best way to check this.

What are the other possibilities that would cause the system pressure to continually rise? Over the past 2 days I have removed about 12 – 15 litres of water by using the PRV and bleeding the rad. I have a call in to a plumber but he said it would be a couple of days before he can get to me. I’m just worried about the water loss to the system, I don’t want to cause any damage…I am using the system sparingly at the moment.

I read from some of the other posts that it may have something to do with the Expansion Vessel. Not quite sure what this does so any information would be appreciated.

If anyone has a link to a website that explains the workings and configuration of a sealed system, it would help me a lot.

Thanks in advance for your help.

 

[IanDB]

The expansion vessel has an airgap and is charged to a pressure of 1bar.

As hot water heats up it expands and if it didn't have anywhere to go it would pressurise the system (you could see this while watching the pressure guage rise as the boiler heats the system up) until it reached the point where the PRV lifts and releases the excess pressure (normally 3 bar).

As air is compressible, when the water heats up it expands into the expansion vessel and the pressure is maintained at 1 bar ( or there abouts). If your airgap has gone due to either loss of air or the diaphram rupturing then the system will react as above. Once the boiler switches off and the system cools down the pressure will be less than orignally seen as water has escaped from the system.

If these are the symptoms then possibly you have a problem with the expansion vessel.

However, this will only occur if the boiler is on. If you are experiencing a pressure rise even with the boiler off then it is probable that the filler loop is letting water into the system (it certainly sounds like it). Also, everything was fine until you opened the filler loop. Have you tried disconnecting it?

 

[galwegian]

Ian,

Thanks for your reply. I agree with you that it's probably the filler loop leaking into the system. The pressure rises even when the system is not on and I noticed a small leak from the wheel when I was checking it a little while ago.

Unfortunately, it's a permanent fixture at the moment with one wheel valve blocking the mains supply. It will have to be replaced properly but I'm not sure how. If I turn off my water supply outside the house this will stop my mains flow into the system. However, I still cannot remove the wheel valve because the water already in the system will drain out. Do I have to drain the whole system to replace the valve?

My intention is to replace the current one wheel setup with a 2 wheel setup joined by a flexible hose. It seems like a pretty straightforward job but my plumbing knowledge is pretty limited so I would need to figure out how to stop the water flow from the system side once the wheel valve is disconnected.

Any thoughts?

Thanks again.

 

[Bahco]

There should be a d check valve connected to your filling loop, (looks like an isolating valve but longer with a small screw in the middle)
This will only allow water in but not out. Have a look, if so you can unscrew the loop leaving the dcv on the pipework and your system full

 

[kevplumb]

bet its two tees and a gate valve

 

[galwegian]

Looks like it may have been a shoddy job...from my angle it looks like it's just a gate valve (which is leaking). I need to remove some casing in the morning to get a better look.

Thanks for your help.

 

[galwegian]

I jig-sawed part of the casing off to get a good look and theres only one red wheel valve (?). This was slightly wet underneath so I tightened the nut just inside the red wheel but still had the leak.

Decided to go for it and tightened it as hard as I could without forcing, it actually turned a lot more than I was expecting. Hopefully this will stop the pressure rising, should know in about an hour.

Thanks to all.

 

[Diyisfun]

IanDB
Posted: :
The expansion vessel has an airgap and is charged to a pressure of 1bar.

How does this air gap get there?

I had a need to partly drain my system, after I finished the job I opened the valve to bring the presure up to 1bar.

Did the fresh water not displace the air gap?

 

[IanDB]

It's charged at time of manufacture. I believe that most (all?)expansion vessels have a rubber diaphram in them. The air is on one side, water on the other. When you fill your system the air compresses to the pressure of the water.

If you drain the water down the air will just push the diaphram out but will go back when re-pressurised.

The thing to watch for if recharging yourself is that you have to do it with no pressure in the system or you don't put enough air in. (The boiler pressure guage monitors water pressure, not the pressure of air in the EV - you have to do that separately.)

 

[sniper100]

Looks like it may have been a shoddy job...from my angle it looks like it's just a gate valve (which is leaking). I need to remove some casing in the morning to get a better look.

Thanks for your help.

I agree its shoddy It is A Water Byelaw now that states The filling loop MUST be removed, and only installed when repressurising the system. If you are capable and I do not mean to offend, you can purchase a filling loop kit. I hope this helps. One other thing if the gate valve is leaking from the actual gland nut (where the spindle is attached) tighten the gland nut slightly.

 

[Diyisfun]

Ian...thanks for that.