Combi boiler system losing pressure

[Grahamwilliam]

Hopefully some of the experts can give me badly needed advice. Over past year my combi system has been losing pressure from 1.5bar to 0.25bar every 3 days. Therefore i have been re pressuring the system to 1.5 bar every 3 days. I have never been able to find any leaks or weeping of joints on any radiator or connections under the floor. PRV valve seems to be ok as well. So i called the plumber and he suggested replacing the expansion unit which we did, and now it is fitted the system pressure only lasts 1 days now before i have to re pressure up to 1.5 bar from 0.25 bar. the new expansion units seems to have made it worse and plumber believes the old expansion unit bladder was punctured. i have checked all rads, underfloor and boiler again and can find no leaks or weeping, help, please any ideas anyone?

 

[Puddle]

what make of combi is it

 

[Blackcatgas]

Hopefully some of the experts can give me badly needed advice. Over past year my combi system has been losing pressure from 1.5bar to 0.25bar every 3 days. Therefore i have been re pressuring the system to 1.5 bar every 3 days. I have never been able to find any leaks or weeping of joints on any radiator or connections under the floor. PRV valve seems to be ok as well. So i called the plumber and he suggested replacing the expansion unit which we did, and now it is fitted the system pressure only lasts 1 days now before i have to re pressure up to 1.5 bar from 0.25 bar. the new expansion units seems to have made it worse and plumber believes the old expansion unit bladder was punctured. i have checked all rads, underfloor and boiler again and can find no leaks or weeping, help, please any ideas anyone?

The hot water plate heat exchanger could be letting the water out through the hot tap. re presure the boiler make sure the heating isnt set to come on etc,take your Mrs away for the weekend The Malmaison hotel in Oxford is nice, come back and see if its still at 1.5 bar.

 

[payney1974]

Why would you change the expansion vessel if the prv wasnt passing?

 

[Grahamwilliam]

Thanks Puddle, the combi make is 'Vokera Linea max'

Thanks for getting back to me Blackcatgas. i tried your suggestion last week and the gauge was at zero when i came home 2 days later. heating had not been on.

The other thing that is strange is that when i boost the pressure up to 1.5 bar, and heating is on, the pressure remains constant at 1.5bar for 12 hours or so, then in a period of 2-3 hours (while heating is still on) it drops rapidly from 1.5 bar to 0

 

[John Flower]

Not really aufait with Vokeras, if it is a condensing boiler then their might be an internal leak that is draining unoticed by the condensate. If not then there has to be a leak somewhere. Have you checked the aav in the boiler ect . Are you definately sure that the prv is not letting by,as the tiniest bit of debris can hold the valve from its seating.

 

[Grahamwilliam]

Thanks John, i have a bag on the PRV but it is dry a a bone. seems like that is ok.
i have also been running a test for the last 18 hours and only have the hot water on and central heating off. the pressure is constant at 1.5 bar. therefore it seems that when the heating is on i lose pressure after a period of time, but when only the hot water is on the pressure is steady

 

[John Flower]

Then the leak is on the central heating side, possibly on a joint or fitting downstairs as you would notice the water through the ceiling.
You need to trace the pipework and look at joints ect. In the year previous have you had any thing done that would of involved fixing things to the floors ,as a fixing might of nicked a pipe to cause a leak.

 

[Grahamwilliam]

john, i was thinking the same, but what do you think would explain why pressure would remain constant for 12 hours while the heating was on and then after 12 hours pressure drops away while heating is still on to 0 bar? See the thread posted at 12.03 today

 

[coldwrench]

I am having the almost identical problem with my Vokera Mynute 20SE. (Bagged the PRV pipe just as you did!!)

I have replaced a litany of components in the system but I still have the leak. (See most recent post by coldwrench)

I’m with you on the ‘under floor leak’, I just don’t believe I have one. It’s always possible, but I think unlikely). Frustration got the better of me last night. I opened the sealed chamber and manoeuvred a flashlight around to try view the state of the heat exchanger. The pipe unions on the outside of the chamber were pristine. However, inside the chamber both flow and return ends of the exchanger were rusted. I’m now convinced the water is leaking into the chamber and burning off when the heat is on.

I have little left to replace in the system except the heat exchanger. My leak isn’t as bad as yours, so I’m going to struggle on to the spring/summer and remove the heat exchanger. Depending how that goes, I’ll either replace it or replace the boiler. Not sure yet.

Have you considered your CH heat exchanger?

 

[Transcoman]

john, i was thinking the same, but what do you think would explain why pressure would remain constant for 12 hours while the heating was on and then after 12 hours pressure drops away while heating is still on to 0 bar? See the thread posted at 12.03 today

l had an interesting yet similar problem to trace when l was called out to a system losing pressure; the problem was similar, pressure held whilst heating was on but lost pressure when it was off. The loss of pressure was eventually tracked down to a poorly fitted compression fitting under the floor in the hallway.

As the heat expanded the copper tube and olive, the joint was made but as it contracted due to cooling then the pressure dropped. There was a lot of debris beneath the floorboards which soaked most of the water up, it doesn't take a great deal for the pressure to drop to zero.

 

[john.bell55]

I had Vokera problems as well. Turned out the heat exchanger was cracked and need replaced...Problem solved

 

[stevetheplumber]

belive me you would know if the heat exchanger was gone enough to drop the preasure that much you need to find the leak you may have to preasure test the system to find it

 

[coldwrench]

I had Vokera problems as well. Turned out the heat exchanger was cracked and need replaced...Problem solved

Can you describe to us the nature of the pressure loss?

How fast did the pressure drop? Did you have water leaking from boiler or was it leaking/evaporating when heat on?

Thanks.

 

[john.bell55]

The system needed topped up every other day, losing about 1 bar. it sounded as if it was kettling.
There was a hairline crack on the heat exchanger which when changed solved the pressure loss. Before changing the heat exchanger I checked the whole system for leaks as this was the most obvious and least expensive option and explanation. Before going down this road I would take stevetheplumbers advice and pressure test the system. There was no obvious leak at the heat exchanger as most of water evaporated, however now and again I noticed a small drip and thought it was a compression joint in the pipes into the boiler.

 

[peteh20]

you can put a presure guage on a rad presure your system up (both guages will read the same) then isolate the system out using the isovalves under the boiler leave overnight any leak on your system will be shown on the rad guage a boiler leak will show on the boiler guage. I ve had a leak on an auto air vent within a combi which evapourated within the boiler took a while to find it. doing this test will at least make sure your looking in the right place good look

 

[coldwrench]

you can put a presure guage on a rad presure your system up (both guages will read the same) then isolate the system out using the isovalves under the boiler leave overnight any leak on your system will be shown on the rad guage a boiler leak will show on the boiler guage. I ve had a leak on an auto air vent within a combi which evapourated within the boiler took a while to find it. doing this test will at least make sure your looking in the right place good look

I would like to do that but I already tried to close them when changing the pump. They wouldn’t turn easily through 90 degrees and leaked when returned to the open position. Fortunately, the leaking stopped after 1~2 days. The way the original piping was installed means fitting separate valves is not very easy. It’s probably easier to follow the heat exchanger route, but I will certainly give that suggestion some more thought.

 

[Blackcatgas]

I would like to do that but I already tried to close them when changing the pump. They wouldn’t turn easily through 90 degrees and leaked when returned to the open position. Fortunately, the leaking stopped after 1~2 days. The way the original piping was installed means fitting separate valves is not very easy. It’s probably easier to follow the heat exchanger route, but I will certainly give that suggestion some more thought.

Tighten up the packing glands if they leak.