Losing pressure in Central Heating system - going crazy!

ThisIsWeird

cheme7676 said:

ThisIsWeird said:

Hi Cheme.
Darned annoying, eh?! There was another recent thread with the same head-scratching issue - not sure how that turned out.
You've had a few repairs carried out on you boiler recently, but there's no reason to suspect any connection with this.
When you top up the pressure, how much water do you think is being fed in?! Hard to know, but surely a good few seconds of 'hisss'?! That must surely be at least a cupful of water? I'm guessing that if this is a leak from a pipe, joint or radiator, it'll be bludy noticeable. So I'm equally guessing that you just haven't come across it yet...
Or, it's escaping some other way. The one thing you haven't mentioned is the condensate pipe. This can be awkward to monitor as water comes out in normal use, and you have seemingly no loss when the boiler ain't running.
Hmmmm, I wonder if smellies added to the water could be a great idea?! You'd be focussing on this pipe, so it should be obvious if system water is also coming out there. 
Assuming the smelly wouldn't cause any harm to internal parts - I can't imagine a small amount would - then you'd need to set up the condensate outlet to empty into a loose-lidded container so it's caught and can be sniffed.
Now, are there such smelly additives?!
Is you system pressure pretty stable in use - does it fluctuate much up and down with temp?

It’s honestly the worst and super stressful. I would be less stressed if my isolation test on the boiler proved the HX was faulty and the whole thing needed replacement!

I don’t know the answer to that, but I know how much water is coming out when I bleed the radiators. So draining around 300ml from a radiator gave me approximately 0.2 bar of pressure loss when I checked it on a cold system a few days ago. So definitely at least a cupful when topping up after an F1 fault.

I agree with the noticeable comment however if the leak only occurs when the system is hot, it tells me that it’s probably evaporating too quickly (considering this is a relatively slow leak) which makes it harder to catch.

Boiler is pretty stable when in operation yeah. I don’t see any fluctuations. I get around a 0.4 bar increase from cold to hot once CH is turned in.

i can add some perfume for sure and monitor. I’m back at the house next week and will check out some videos of others who have done it and try my luck. I can’t get a container under the condensate pipe because it’s so close to the drain in the ground there is hardly clearance. Could I wait for a dry day and put some paper or something on the ground and smell it after a few hours or something like that?

I'd suggest that a 1bar drop over 5ish days would not just evaporate, at least not right away. I guess it could dry out over a day or so when the boiler isn't in use, but once you locate the leak, I think it should be obvious - stains, scale build up, discolouration.
Whether, say, a plasterboard ceiling could cope with this without it staining is also unlikely, imv, but I guess not impossible.
Hidden behind a wall, then it could well not show if it drips harmlessly to ground.
The fact it seemingly occurs when the boiler is at full heat does suggest an expanding faulty part, and the most obvious culprit is, I guess, the MainX. I could see this happening with some copper joints, soldered and compression too, but I suspect less likely.
You have mostly plastic pipes and fittings - hmm, to me these usually work or fail, yes sometimes drip, but would the drip increase with heat? Possibly, but just doesn't seem so likely.
Other possibilities - the P2P can perforate, but that would have the opposite effect - the mains pressure would raise your system's.
I'd want to add as little smelly as would work, but you would need to capture the condensate for this. Does the pipe disconnect as it leaves the boiler anywhere? Would you be 'happy' to even cut it and fix it afterwards using a 22mm solvent coupling?
If the condensate simply disappears into the ground or drain, no idea what your chances are. I guess it might point to a different part of the house, tho'!
Add stuff, close all room doors, and go for a fresh air walk for at least a half-hour?

cheme7676

ThisIsWeird said:

cheme7676 said:

ThisIsWeird said:

Hi Cheme.
Darned annoying, eh?! There was another recent thread with the same head-scratching issue - not sure how that turned out.
You've had a few repairs carried out on you boiler recently, but there's no reason to suspect any connection with this.
When you top up the pressure, how much water do you think is being fed in?! Hard to know, but surely a good few seconds of 'hisss'?! That must surely be at least a cupful of water? I'm guessing that if this is a leak from a pipe, joint or radiator, it'll be bludy noticeable. So I'm equally guessing that you just haven't come across it yet...
Or, it's escaping some other way. The one thing you haven't mentioned is the condensate pipe. This can be awkward to monitor as water comes out in normal use, and you have seemingly no loss when the boiler ain't running.
Hmmmm, I wonder if smellies added to the water could be a great idea?! You'd be focussing on this pipe, so it should be obvious if system water is also coming out there. 
Assuming the smelly wouldn't cause any harm to internal parts - I can't imagine a small amount would - then you'd need to set up the condensate outlet to empty into a loose-lidded container so it's caught and can be sniffed.
Now, are there such smelly additives?!
Is you system pressure pretty stable in use - does it fluctuate much up and down with temp?

It’s honestly the worst and super stressful. I would be less stressed if my isolation test on the boiler proved the HX was faulty and the whole thing needed replacement!

I don’t know the answer to that, but I know how much water is coming out when I bleed the radiators. So draining around 300ml from a radiator gave me approximately 0.2 bar of pressure loss when I checked it on a cold system a few days ago. So definitely at least a cupful when topping up after an F1 fault.

I agree with the noticeable comment however if the leak only occurs when the system is hot, it tells me that it’s probably evaporating too quickly (considering this is a relatively slow leak) which makes it harder to catch.

Boiler is pretty stable when in operation yeah. I don’t see any fluctuations. I get around a 0.4 bar increase from cold to hot once CH is turned in.

i can add some perfume for sure and monitor. I’m back at the house next week and will check out some videos of others who have done it and try my luck. I can’t get a container under the condensate pipe because it’s so close to the drain in the ground there is hardly clearance. Could I wait for a dry day and put some paper or something on the ground and smell it after a few hours or something like that?

I'd suggest that a 1bar drop over 5ish days would not just evaporate, at least not right away. I guess it could dry out over a day or so when the boiler isn't in use, but once you locate the leak, I think it should be obvious - stains, scale build up, discolouration.
Whether, say, a plasterboard ceiling could cope with this without it staining is also unlikely, imv, but I guess not impossible.
Hidden behind a wall, then it could well not show if it drips harmlessly to ground.
The fact it seemingly occurs when the boiler is at full heat does suggest an expanding faulty part, and the most obvious culprit is, I guess, the MainX. I could see this happening with some copper joints, soldered and compression too, but I suspect less likely.
You have mostly plastic pipes and fittings - hmm, to me these usually work or fail, yes sometimes drip, but would the drip increase with heat? Possibly, but just doesn't seem so likely.
Other possibilities - the P2P can perforate, but that would have the opposite effect - the mains pressure would raise your system's.
I'd want to add as little smelly as would work, but you would need to capture the condensate for this. Does the pipe disconnect as it leaves the boiler anywhere? Would you be 'happy' to even cut it and fix it afterwards using a 22mm solvent coupling?
If the condensate simply disappears into the ground or drain, no idea what your chances are. I guess it might point to a different part of the house, tho'!
Add stuff, close all room doors, and go for a fresh air walk for at least a half-hour?

Yeah I can pull condensate outlet pipe from under the boiler, so I can use that. Also I am able to get a polybag around the condensate outlet without the need to cut and repair. 2 options there I guess

good plan, and one for me to try when I’m back next week for sure. 

ThisIsWeird

Obviously don't leave the poly bag secured tightly for any length of time

I'd be tempted to buy a wee bottle of the 'essential oils' stuff you add to air freshener stalks - very concentrated oily stuff, and add just 5-10ml or so.

I wonder what a good smell choice would be? Something distinctive and that wouldn't be confused with naturally-occurring smells such as pine?

And the rest you can use in the house afterwards :-)

FreeBear

ThisIsWeird said: I wonder what a good smell choice would be? Something distinctive and that wouldn't be confused with naturally-occurring smells such as pine?

Hydrogen Sulphide - Very distinctive smell that you will never confuse with anything else. And trust me, you will not want to smell the stuff neat (it is a tad toxic).

Albermarle

You do not say if it is a Combi boiler, or if you have a separate hot water tank?

Anyway in either case does the pressure still drop, when you run the boiler for the hot water part on its own?

I have no idea what might be causing the problem, but the above may help to eliminate possible problem areas.

ThisIsWeird

Albermarle said:

You do not say if it is a Combi boiler, or if you have a separate hot water tank?

Anyway in either case does the pressure still drop, when you run the boiler for the hot water part on its own?

I have no idea what might be causing the problem, but the above may help to eliminate possible problem areas.

Ideal Logic Combi 35

born_again

Wrap some tissue or kitchen roll round the joints you can get to. Will soon tell you if you have a leak there.
We had one that was leaking out of the bottom of a TRV. Only picked up by noticing damp kitchen roll.

MouldyOldDough

We had a similar problem with our Worcester combi boiler a few years ago - it was constantly needing topping up - but we could not find any leaks anywhere

Eventually we found a gas engineer (not fitter or installer) who had been trained by Worcester who fitted an eternal pressure vessel - this solved the problem for good !

ThisIsWeird

MouldyOldDough said:

We had a similar problem with our Worcester combi boiler a few years ago - it was constantly needing topping up - but we could not find any leaks anywhere

Eventually we found a gas engineer (not fitter or installer) who had been trained by Worcester who fitted an eternal pressure vessel - this solved the problem for good !

You clearly hadn't noticed that your system pressure was shooting up every time the CH was turned on
Sadly, seemingly not cheme's issue.

ThisIsWeird

A thought, tho', Cheme. When you isolated the F&R CH pipes from the boiler, did you keep on using it to deliver DHW?
If not, worth doing. Monitor the boiler during a good 5-minute shower. Note starting, running, and end pressures.