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Can anyone offer any advice on a total mystery pressure loss on a Vaillant Eco Pro 28 combi boiler? Here's the background:

Almost total pressure loss every 1-2 hours. Apparently the equivalent of several pints of water each time
When pressure is up, heating and hot water functioning fine, so flame and water/heat switch fine. PRV also working fine. No water inside boiler chamber anywhere
Expansion chamber has been replaced: no change in problem
Isolator valves fitted to heating in/out pipes, so when isolated, the boiler does not lose pressure (indicating a leak elsewehre therefore?)
BUT: Professional leak detection not found any evidence of leak over course of 2 days monitoring (8 hours each). Including CCTV investigation, thermal imaging. Gas tracing so far ineffective as some pipes are in a void underneath suspended floor

Have we missed trying any other angle? All the professionals are stumped (3 separate gas engineers and 1 professional leak tracer) Cheers!
 
Internal leak inside the heat exchanger chamber which then runs into the condense drain so you dont see it get a GSI in strip down the burner and condense pipe into a container pressurise it up he will know I had this on the exact same boiler a few years ago the heat exchanger was a mess inside and combustion was a problem worth a try ? If it then proves to be ok then it must be externally on the pipework somewhere. Regards Kop
 
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Cheers for that. Couple of questions
  • if that was the case, wouldn't the water coming out via the condenser pipe be hot? We've had the pipe off, and no major water exit via that route
  • we've isolated the heating system (the last GSI fitted isolator lever valves): when the heating system is isolated but hot water still available, and called-for, there is no drop of pressure. Have also done this overnight, pressure remained constant for 10hrs. Surely pressure would continue to drop during hot water running? We're talking about 05 litre per hour, that's quite a bit of water..
 
Can anyone offer any advice on a total mystery pressure loss on a Vaillant Eco Pro 28 combi boiler? Here's the background:

Almost total pressure loss every 1-2 hours. Apparently the equivalent of several pints of water each time
When pressure is up, heating and hot water functioning fine, so flame and water/heat switch fine. PRV also working fine. No water inside boiler chamber anywhere
Expansion chamber has been replaced: no change in problem
Isolator valves fitted to heating in/out pipes, so when isolated, the boiler does not lose pressure (indicating a leak elsewehre therefore?)
BUT: Professional leak detection not found any evidence of leak over course of 2 days monitoring (8 hours each). Including CCTV investigation, thermal imaging. Gas tracing so far ineffective as some pipes are in a void underneath suspended floor

Have we missed trying any other angle? All the professionals are stumped (3 separate gas engineers and 1 professional leak tracer) Cheers!
I have read the above. 1. combi boiler pressure loss to zero in an hour or so, thats usually about 4 litre
on a standard system. 2. Pressure relief valve not passing..have you done the condom over the outside end test to see if it fills up. 3. Condensate and hex not crossed. 4 When you fill system and isolate boiler ...sure...the boiler stays at 1.5 bar. 5. Then it can only be the pressurised ch circuit
4 litres of water in two hours is a large volume to hide. So it not upstairs its not near any carpets etc.
its also unlikely to be in a stud wall.
A. Have you got solid floors, wood suspended or block and beam ?
B. Any work carried out recently
I would close off all the rads at both ends, close off the boiler and blow it up as far as your mains pressure will go and make it show itself. Looking is one thing but listening is great. let me know how
you get on ......centralheatking
 
I have read the above. 1. combi boiler pressure loss to zero in an hour or so, thats usually about 4 litre
on a standard system. 2. Pressure relief valve not passing..have you done the condom over the outside end test to see if it fills up. 3. Condensate and hex not crossed. 4 When you fill system and isolate boiler ...sure...the boiler stays at 1.5 bar. 5. Then it can only be the pressurised ch circuit
4 litres of water in two hours is a large volume to hide. So it not upstairs its not near any carpets etc.
its also unlikely to be in a stud wall.
A. Have you got solid floors, wood suspended or block and beam ?
B. Any work carried out recently
I would close off all the rads at both ends, close off the boiler and blow it up as far as your mains pressure will go and make it show itself. Looking is one thing but listening is great. let me know how
you get on ....centralheatking
Thanks for all of this; I'm tending towards the leaking in CH circuit somewhere, as there's no leakage from PRV exit or abnormal amounts of condensate. We have suspended floors in most of downstairs (wood beams). We had an extension built/kitchen renovated earlier this year, all the plumbing in the new part is push fit plastic. Leak detector thinks he has narrowed it down to somewhere within the new area, but the void below suspended floor is up to 80cm deep (we built onto a patio area below the level of the house), so he's finding it difficult to trace, and can't get the camera in far enough because there's a sh**load of insulation in the way. Floors coming up next week if he can;t get any further with a gas detection :-(
Not sure what you mean about 'blowing it up'; do you mean seal off the rads and then repressurise the system from mains water until the PRV kicks in ??
 
Thanks for all of this; I'm tending towards the leaking in CH circuit somewhere, as there's no leakage from PRV exit or abnormal amounts of condensate. We have suspended floors in most of downstairs (wood beams). We had an extension built/kitchen renovated earlier this year, all the plumbing in the new part is push fit plastic. Leak detector thinks he has narrowed it down to somewhere within the new area, but the void below suspended floor is up to 80cm deep (we built onto a patio area below the level of the house), so he's finding it difficult to trace, and can't get the camera in far enough because there's a sh**load of insulation in the way. Floors coming up next week if he can;t get any further with a gas detection :-(
Not sure what you mean about 'blowing it up'; do you mean seal off the rads and then repressurise the system from mains water until the PRV kicks in ??
Blow the system up...close off the flow and return to this boiler, close off both sides of each radiator, just to narrow things down and reduce the volume of water involved. Then connect the filling loop from cold main into heating system forget what pressure just let it go as high as your supply will go. Then see what happens...the leak should show itself but as I stated dont just look listen .
I have a lot of experience with pressurised domestic heating systems but the rules pre clude
any self promotion which I am happy with....centralheatking
 
How big is the system, is the expansion vessel big enough to cope?

If it wasn't big enough that would show at the pressure relief valve. OP says it's dry there. I'd still want to do a test on that and put the finger of a rubber glove over the end of the discharge pipe, held in place with a rubber band. That would 100% eliminate the PRV passing from being the problem.
 
Thanks all. Non-specialist's question just to eliminate the hex thing: if the CH circuit is isolated (using lever valves) but the HW is still operating normally and there's no pressure loss (remained constant for 8 hrs overnight) , does that eliminate the heat exchanger 100%? The PRV outlet is dry (as is the wall by the pipe), and no loss of heat/pressure when it's HW-only operation
 
I would say system leak then
 
Thanks all. Non-specialist's question just to eliminate the hex thing: if the CH circuit is isolated (using lever valves) but the HW is still operating normally and there's no pressure loss (remained constant for 8 hrs overnight) , does that eliminate the heat exchanger 100%? The PRV outlet is dry (as is the wall by the pipe), and no loss of heat/pressure when it's HW-only operation

Thanks for eliminating the PRV outlet because I've lost count of the times people have told me "It's definitely not that" and that's exactly what it turned out to be!
 
Thanks. I just can't understand why we or the leak specialist can't detect 2-4 litres an hour of water escaping anywhere? It's got to come out somewhere right, even if there is a void under the suspended floor?

It can be amazing how much water a building can take before it shows sometimes. CHK's suggestion of isolating the boiler and increasing the pressure is suggested because it will hopefully speed up the process of getting the leak to show. It sounds dodgy on the face of it, putting more water into the building but that's probably what's happening anyway and ultimately it'll show when it shows and the overall amount of water escaping will be more or less the same either way.

Also, his suggestion of listening for the leak is a good one. At a higher pressure the leak should be a bit noisier and therefore easier to detect by listening. You'll need to do it at a quiet time though.
 
It can be amazing how much water a building can take before it shows sometimes. CHK's suggestion of isolating the boiler and increasing the pressure is suggested because it will hopefully speed up the process of getting the leak to show. It sounds dodgy on the face of it, putting more water into the building but that's probably what's happening anyway and ultimately it'll show when it shows and the overall amount of water escaping will be more or less the same either way.

Also, his suggestion of listening for the leak is a good one. At a higher pressure the leak should be a bit noisier and therefore easier to detect by listening. You'll need to do it at a quiet time though.
cheers for that. In a house with two teenagers and a gerbil, that's easier said than done :) . Leak guy is coming back tomorrow, I will suggest it to him (although he's already spent a day here with us all being out, and with sensitive microphones, and still not found it.
 
cheers for that. In a house with two teenagers and a gerbil, that's easier said than done :) . Leak guy is coming back tomorrow, I will suggest it to him (although he's already spent a day here with us all being out, and with sensitive microphones, and still not found it.
My money is in the under block and beam floor...so install a couple of ball o fix 22mm or 15 mm where the flow and return go in and out.Turn them to off. Put a pressure test on 2 bar for 24 hrs and see what happens if it holds its under the floor if it drops then let me know... two ballo fix dead cheap and take them out when you are sorted. Microphones huh window dressing for the desperate in my opinion !
centralheatking
 
My money is in the under block and beam floor...so install a couple of ball o fix 22mm or 15 mm where the flow and return go in and out.Turn them to off. Put a pressure test on 2 bar for 24 hrs and see what happens if it holds its under the floor if it drops then let me know... two ballo fix dead cheap and take them out when you are sorted. Microphones huh window dressing for the desperate in my opinion !
centralheatking
Thanks. Already have lever valves installed to F&R and have set these to off overnight, pressure maintained for 8-10 hours with no drop, so it must be under the floor.
 
Thanks. Already have lever valves installed to F&R and have set these to off overnight, pressure maintained for 8-10 hours with no drop, so it must be under the floor.
Put a camera and a life jacket on the gerbil and make it earn its keep. So you know where the leak its not nice. How much depth below the block and beam set up ? forget the mic idea not even nasa will pick it up under block and beam and you know its there anyway. put a diagram up of the layout, rads and the bulding generally.
chking
 
Put a camera and a life jacket on the gerbil and make it earn its keep. So you know where the leak its not nice. How much depth below the block and beam set up ?
chking
It's a suspended wood beam floor, depth to ground is up to 80cm in places. But the pipework is new (plastic pushfit), and isn't that deep under the insulation, maybe 30-40cm at most (it's a new extension)
 
Microphones huh window dressing for the desperate in my opinion !
centralheatking

I respectfully disagree. Nothing wrong with using the old Mk. I eyeballs and earholes but if the microphone can pick up something the old meaty bits can't it's still a win and the leak is found either way (hopefully!).
 
I respectfully disagree. Nothing wrong with using the old Mk. I eyeballs and earholes but if the microphone can pick up something the old meaty bits can't it's still a win and the leak is found either way (hopefully!).
my money is on the gerbill plan !
[automerge]1575391568[/automerge]
It's a suspended wood beam floor, depth to ground is up to 80cm in places. But the pipework is new (plastic pushfit). So just make a few traps, or is your floor lovely or laminated ? chking
 
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my money is on the gerbill plan !
[automerge]1575391568[/automerge]
It's newly fitted laminate (last 5 months). Not glued however. Not block n beam, but just wooden joists, planking and chipboards over insulation, then two thin 2mm layers of under-floor membrane (foam/plastic), then laminate on top. Sorry no diagrams available
 
You can buy a stethoscope off Amazon for under 5 pounds. I have used 1 for similar reasons. An automotive stethoscope is great for detecting flow in a pipe you can't access.
 

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