boiler losing pressure - ch pipes not leaking.

[darriusdax]

Hi guys, My client has a leak on this system. It is a big house with 21 radiators all fed by this condensing Remeha condensing boiler. He has had the Remeha approved installers out to diagnose the boiler, they say that there is no leak outwith the pipes, so we isolated the pipe work and put tracer gas in - we got no significant readings any where in the house, and more telling, the gas pressure did not drop over the 2 hrs we had it up at 2.5 bars. ( the client has been losing 1.2 bar per day.) - gas particles are smaller and should leak more easily.
So if there is no leak in the pipes, is there anything that the remeha techs could have missed, and what are the different causes of pressure loss in a condensing boiler system.

Thanks in advance of your advice guys.

 

[Jay Jay]

Main hex leaking through condense quite common now Adays
Good luck

 

[Scott_D]

A leak that only occurs when hot?

 

[darriusdax]

Main hex leaking through condense quite common now Adays
Good luck

thanks jay jay

 

[darriusdax]

A leak that only occurs when hot?

No. the client says that the pressure loss is intermittent, seems to lose pressure worse when the system is cooling down. we did think screw in pipe... but no loss on pipe test. We are going back today to put the pipe system under pressure for a week - independent test with the flow and return isolated in boiler room.
Cheers.

 

[Chuck]

Have you checked what's coming out of condensate drain for the presence of inhibitor, which would indicate a HEX leak?

 

[Darren Jackson]

As Jay Jay pointed out Hex leaking into condense, come across this a few times now. Also quite common is the PRV letting by or flat expansion vessel activating the PRV.

 

[darriusdax]

Have you checked what's coming out of condensate drain for the presence of inhibitor, which would indicate a HEX leak?

good call - would that leak pressure from the main closed ch loop ?

 

[darriusdax]

good call - would that leak pressure from the main closed ch loop ?

Would it be mental to put a we bit of drain dye in the system and then check condensate? just realised i replied to myself..... noob

 

[SimonG]

Pressurised system? Expansion vessel ok? Pressure relief ok?

 

[bright spark]

Leak on exchanger with boiler running maybe. Going down condense drain. Or possibly a leak in cylinder coil.
It would be normal for pressure t drop when cooling especially if exp vessel pressure incorrect

 

[ShaunCorbs]

Your only way isolate boiler from system

And pressure test system to 6 bar if no drop it's the boiler

But I think there will be a drop

 

[darriusdax]

Your only way isolate boiler from system

And pressure test system to 6 bar if no drop it's the boiler

But I think there will be a drop

Interesting... when I pulled the flexi off the condensate and piped it in to a bucket then fired up the system from cold, we got about 2 litres of water in an hour... this seems a hell of a lot. Other information, he has a 50 litre expansion vessel for 2 floors , 21 large radiators in total.
I have been today and stuck a pressure gauge on a towel rail, isolated the flow and return at the boiler, and left the loop heating the hot water cylinder ( the ch thermostat is set to 5, so it should not kick in at all )
I have set it at 2 bar because there are some old compression fittings in the system that I dont want to blow.
So the boiler is being tested at the same time as the ch loop being isolated. I will update on the results.
Thanks for all your help so far guys.

 

[ShaunCorbs]

Interesting... when I pulled the flexi off the condensate and piped it in to a bucket then fired up the system from cold, we got about 2 litres of water in an hour... this seems a hell of a lot. Other information, he has a 50 litre expansion vessel for 2 floors , 21 large radiators in total.
I have been today and stuck a pressure gauge on a towel rail, isolated the flow and return at the boiler, and left the loop heating the hot water cylinder ( the ch thermostat is set to 5, so it should not kick in at all )
I have set it at 2 bar because there are some old compression fittings in the system that I dont want to blow.
So the boiler is being tested at the same time as the ch loop being isolated. I will update on the results.
Thanks for all your help so far guys.

i would say thats about right how much condensate it should produce

 

[Jay Jay]

50l vessel wow that's some size??? Id expect a smaller size vessel as if oversized that will cause issues mate

 

[ShaunCorbs]

50l vessel wow that's some size??? Id expect a smaller size vessel as if oversized that will cause issues mate

its not far off (think around 35-40l) and no it wont

 

[Chuck]

we got about 2 litres of water in an hour... this seems a hell of a lot.

That would correspond to 24kW continuous operation and with a decently low return temperature.

 

[darriusdax]

That would correspond to 24kW continuous operation and with a decently low return temperature.

Yep , the system would have been cold as it had been off and just topped up with cold mains.... So I guess it was trying to circulate and heat roughly 300 litres of cold water up to 25 degrees. Still it was surprising to see water literally spurting out of the condensate pipe,

 

[ShaunCorbs]

When the boiler isn't on does it still drip ?

 

[darriusdax]

When the boiler isn't on does it still drip ?

I will check, obviously I am not there... frustrating, I want to call the client, but its just another job at the end of the day. By the way.. I went down the bathroom fitting route then got in to leak detection... boilers is probably my weakest discipline because i never did gas work, getting great results with sewerin audio equipment on external pipe leaks, and a ferret machine which inflates a small balloon at the head of a long cable - pressure behind lets you know when you go past the leak. We could start a leak detection forum on this site so that I can help the other way instead of you lads bailing me out all the time

 

[Chuck]

Still it was surprising to see water literally spurting out of the condensate pipe,

By 'spurting' I asssume you mean the condensate siphon emptying and releasing a cupfull of condensate every few minutes?

My interpretation of the evidence presented so far is that as the system heats up, the pressure rises to the point (P_hot) that something acts as a pressure relief valve. (This could be the 'official' PRV or if could be a cracked joint somewhere, with the HEX as a likely suspect.) The system will then operate happily like this (at P_hot) until it is allowed to cool at which point it will be apparent that water has been lost (pressure drops to P_low).

This would be confirmed if the next time the system heats up the pressure starts at P_low, rises to P_hot again and then drops back down to P_low when cold.

As others have already suggested, an empty/faulty expansion vessel and the PRV are the most common cause of such symptoms.

 

[bright spark]

If you're gonna pressure test boiler only do it t 4 bar. That's d max it'll take according t Quinta Pro brochure. Especially if it's still under warranty.
These exchangers are known t pop their clogs from time to time.
Listen t Shaun, he knows his stuff

 

[dan_the_plumber]

press shraeder valve pin on expensive vessel. Water coming out? Replace Eco vessel.
Test air pressure in expansion vessel...Repressurise as needed.
Has PRV been blowing off? Leave a party balloon over discharge pipe over few days to find out. Replace as needed PRV.
Repressurise boiler...does pressure gauge shoot straight up? No expansion space in vessel.
Is customer Repressurising boiler? What are that setting it to? Fiddlers
Large amount of corrosion in system? Nitrogen produced, leaves system via auto air vent. Pressure drops. Flush and add inhibitor

Dan

 

[king of pipes]

As above the first thing to check is the expansion vessel, on a system like this it will need to be drained to check the internal pressure i would think the charge pressure would measure between 1-2 bar ? depending on meters of head , on a system that size the vessel size would need to be around 36 litres it maybe the one fitted is to small it should not be fitted laying on its side eithier and i would expect it to be red or grey in colour not blue as these ade normally used for potable water ? , all the heating pipework should be insulated and its not a good idea to have a calor gas bottle stored internally in there , check for a gas saftey certificate on the property , check the benchmark in the boiler manual ? something does not look right here. Regards kop.

 

[darriusdax]

As above the first thing to check is the expansion vessel, on a system like this it will need to be drained to check the internal pressure i would think the charge pressure would measure between 1-2 bar ? depending on meters of head , on a system that size the vessel size would need to be around 36 litres it maybe the one fitted is to small it should not be fitted laying on its side eithier and i would expect it to be red or grey in colour not blue as these ade normally used for potable water ? , all the heating pipework should be insulated and its not a good idea to have a calor gas bottle stored internally in there , check for a gas saftey certificate on the property , check the benchmark in the boiler manual ? something does not look right here. Regards kop.

View attachment 30007

aye. the blue expansion is indeed on the cold mains for some reason, the red expansion vessel (50 litre) is out of shot to the right of the picture. we will deffo check this when we go back.
it is one of these awkward ones where the guy has spent a fortune with his boiler repair company and they say that there is no fault in the boiler set up, but from what he has said.. they did not check the expansion vessel, nor the internal coil, nor the hex... they isolated the boiler and tested its pressure cold.. ie not running. that is useless.
we were only brought in to gas test the flow and return within the house - look for a pipe leak...
thanks kop

 

[dan_the_plumber]

Priority checks:
Leaking rad valves
Expansion vessel
Leak on boiler
PRV
Leaking pipe work (usually compression joints)
Nitrogen leaving system
Air ingress

That's it I think

 

[Stoney Ground]

The 2 FI-C elbows on that cylinder look like they have had leaks around them.

If they leak at 70c, your gas test won't detect it if tested cold.

 

[king of pipes]

Leak on the primary coil in the hot water cylinder is another thing worth checking cheers kop

 

[dan_the_plumber]

Leak on the primary coil in the hot water cylinder is another thing worth checking cheers kop

Good call...any tips as to how to do that please?

 

[king of pipes]

Pump some food colouring in the heating system via the filling loop if its shows up in the hotwater then bingo flush out do repairs . cheers kop

 

[darriusdax]

Pump some food colouring in the heating system via the filling loop if its shows up in the hotwater then bingo flush out do repairs . cheers kop

cheers kop. done it... but we are pressure testing the ch loop till wednesday, so if no drop from 2bar we will open up the flow and return and run the system... hope to see yellow hot water
I take it that if the engineer had the boiler open and tested it cold he would not see if the heat exchanger is faulty ???

 

[king of pipes]

Just a proccess of elimination bud all the best finding it cheers kop

 

[dan_the_plumber]

Pump some food colouring in the heating system via the filling loop if its shows up in the hotwater then bingo flush out do repairs . cheers kop

Good idea...Thanks King

 

[SavageW]

Can you loose pressure through an unvented coil from a sealed CH system? I always thought the pressure on the main side of the cylinder being 3bar would if anything over pressurise the CH system an discharge via the PRV as the CH system pressure would only be around 1-1.5 as opposed the 3-3.5 in the cylinder? I'm genuinely curious as I would like to know if I'm wrong no discredit to other people's suggestions

 

[Chuck]

Can you loose pressure through an unvented coil from a sealed CH system? I always thought the pressure on the main side of the cylinder being 3bar would if anything over pressurise the CH system an discharge via the PRV as the CH system pressure would only be around 1-1.5 as opposed the 3-3.5 in the cylinder? I'm genuinely curious as I would like to know if I'm wrong no discredit to other people's suggestions

Your reasoning is correct.

However, it wasn't clear from the original post whether the system was vented or unvented and it's easy to miss such details when they are buried in a thread of more than 30 posts.

 

[dan_the_plumber]

Can you loose pressure through an unvented coil from a sealed CH system? I always thought the pressure on the main side of the cylinder being 3bar would if anything over pressurise the CH system an discharge via the PRV as the CH system pressure would only be around 1-1.5 as opposed the 3-3.5 in the cylinder? I'm genuinely curious as I would like to know if I'm wrong no discredit to other people's suggestions

Yeah it's a fair shout. But what your talking about there is static pressure. As soon as you open a tap now you've dynamic pressure, which is less by about half.
So when you open a hot tap you may see the boiler pressure (heating circuit) fall and then when the hot tap is closed you may see the boiler pressure rise

 

[SavageW]

Your reasoning is correct.

However, it wasn't clear from the original post whether the system was vented or unvented and it's easy to miss such details when they are buried in a thread of more than 30 posts.

I weren't meaning to sound rude,I was more worried I didn't know something that more experienced guys did. It was the OP's pic with the cylinder an the potable water expansion vessel with the PRV terminating into some sort of plant pot that made me assume it was unvented.

 

[SavageW]

Yeah it's a fair shout. But what your talking about there is static pressure. As soon as you open a tap now you've dynamic pressure, which is less by about half.
So when you open a hot tap you may see the boiler pressure (heating circuit) fall and then when the hot tap is closed you may see the boiler pressure rise

cheers Dan, I wouldn't of even thought of that. I'm new to this an still gaining experience but thanks for explaining