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unvented clyinder losing pressure when system is ideal

when my unvented hot water/heating system is losing pressure when it is ideal.
i have got Advantage Cylinder is manufactured in the UK by RM Cylinders and MAIN 15 HEAT boiler.

we have set the central heating and hot water turned off from 10 am to 5 pm.
when I come back and look at the pressure gauge at 5pm, the pressure is 0 bar.
same thing happening in the morning at 5 am that the pressure is 0 bar.
I have to top up the pressure to 1 bar and then boiler starts immediately.

I can't see any water leak on the floor /plaster board rather the outlet pipe outside home no water leak.

any experts advise me on this cause of this issue?
we've checked PVR and expansion vessel and no leak
 

Stigster

Esteemed
Plumber
The system is losing water somewhere. It has to be. I appreciate that you have said there is no leak at the pressure relief valve/discharge point but this must be 100% verified. Cut a finger off a disposable glove and put it over the end of the pressure relief pipe. Secure it with a bit of tape or a rubber band.

Fill your system to about 1.5 bar pressure and use as normal. Check the D2 when pressure drops next time. The glove finger will burst or come off if this pipe discharges. If it's not this we can look elsewhere. Many times I have been told the PRV has not discharged and I have proved it does. Many times I have been proved it's not that too! It's an easy test though.

People expect to see lots of water or at least evidence of it at the discharge pipe but in reality it can be as little as a few litres in just a few seconds. This can easily disappear by the time you check. Eliminate this first.

If it's not the PRV then there is water escaping elsewhere and it needs tracking down. We will do our best to help.
 
thank you very much sir.
I wanted to let you know what we did was that. we had a water in D2 (discharge pipe outside of building.
we then found out that PVR was discharging water and put in a new PVR where we have a gauge.
we can still see that pressure is losing. we can't see any water leaking on the floor though.
 
Expansion vessel needs looking at.
The Pumber looked at the expansion valve and re pressured.
He now says that the system needs leak seal fluid
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Do you have a non return valve on the filler?
I have mangnet filter but no non return value on that filter
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The Pumber looked at the expansion valve and re pressured.
He now says that the system needs leak seal fluid
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I have checked magnet filet and I can see two black knobs facing each other
I believe that is the non return value.
Yes I have
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I am sorry sir
I have looked at the magnet filter.
I can see two black knob facing each other.
So I believe that is two non return valve.
Can you advise further please
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Do you have a non return valve on the filler?
Sir
I have looked at the magnet filer and can see two black knobs facing each other so I believe yes I have non return valve.
Can you please advise further.
Attached is the picture of magnet filter
 

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Stigster

Esteemed
Plumber
I would not use a leak sealer as a repair as that is a last resort to keep a system going temporarily until a better solution can be found. Using that might work for a while but only to delay the inevitable.

If you are now certain the PRV is not passing water, the leak must be on the heating system somewhere. One possibility is a small leak in the cylinder coil but that is highly unlikely. The cylinder will be almost certainly at a higher pressure than the heating system so any transfer of water there is likely to increase the pressure in the heating side rather than decrease, until the PRV goes but you have eliminated that.

The next thing I would do is to try to force the leak to show somewhere. I'd top up the heating pressure to 2 bar for a couple of days and see if the leak shows somewhere. The water has to be going somewhere. Unfortunately buildings can often take a surprising amount of water before it shows. It only takes a few litres of water lost to drop the pressure below operating pressure.
 
I would not use a leak sealer as a repair as that is a last resort to keep a system going temporarily until a better solution can be found. Using that might work for a while but only to delay the inevitable.

If you are now certain the PRV is not passing water, the leak must be on the heating system somewhere. One possibility is a small leak in the cylinder coil but that is highly unlikely. The cylinder will be almost certainly at a higher pressure than the heating system so any transfer of water there is likely to increase the pressure in the heating side rather than decrease, until the PRV goes but you have eliminated that.

The next thing I would do is to try to force the leak to show somewhere. I'd top up the heating pressure to 2 bar for a couple of days and see if the leak shows somewhere. The water has to be going somewhere. Unfortunately buildings can often take a surprising amount of water before it shows. It only takes a few litres of water lost to drop the pressure below operating pressure.
Thank you sir.
Other plumber mentioned that same that the pressure inside the coil in cylinder is lower than water in tank so the water would go from tank to coil not other way around.

but is therea method or way to check if there is a leak inside coil in cylinder?
Other plumber mentioned non return valve in manger filter - would non return valve attached to magnet filter needs looking at.

Low pressure issue been there for about 6 months and can’t see any leak
 

Stigster

Esteemed
Plumber
Yes, in a typical installation the pressure in the hot water cylinder would be around 2.5 to 3.0 bar. The heating system should be 1.0 to 1.5 bar cold and rise a little when heating is on. So, under most circumstances a hole in the cylinder coil will let water into the heating side and increase the pressure there which is why I don't think it is that.

However to test the coil you need to isolate it somehow. Drain the heating system, empty the coil (not the stored hot water) and disconnect the coil flow and return to see if water is coming from the cylinder coil tappings and keeps coming, being fed from the stored hot water side. I always fit full-bore isolating valves on cylinder coil pipework to make maintenance and cylinder changes easier but I suspect you won't be so lucky to have valves on your cylinder coil, near the cylinder? If you do it becomes a lot simpler.

I think it unlikely to be the coil for reasons already stated but that's how it's done.

Is the boiler a condensing model? I am unfamiliar with UK gas boilers (I only worked on oil systems) but if it's a condenser then it may be possible for a leak path to occur between the boiler and the condensation system. Any thoughts from anyone reading this on that scenario?
 
Yes, in a typical installation the pressure in the hot water cylinder would be around 2.5 to 3.0 bar. The heating system should be 1.0 to 1.5 bar cold and rise a little when heating is on. So, under most circumstances a hole in the cylinder coil will let water into the heating side and increase the pressure there which is why I don't think it is that.

However to test the coil you need to isolate it somehow. Drain the heating system, empty the coil (not the stored hot water) and disconnect the coil flow and return to see if water is coming from the cylinder coil tappings and keeps coming, being fed from the stored hot water side. I always fit full-bore isolating valves on cylinder coil pipework to make maintenance and cylinder changes easier but I suspect you won't be so lucky to have valves on your cylinder coil, near the cylinder? If you do it becomes a lot simpler.

I think it unlikely to be the coil for reasons already stated but that's how it's done.

Is the boiler a condensing model? I am unfamiliar with UK gas boilers (I only worked on oil systems) but if it's a condenser then it may be possible for a leak path to occur between the boiler and the condensation system. Any thoughts from anyone reading this on that scenario?
Yes my boiler is condensing boiler
Ie I have discharge pipe from boiler and stream is condensated
 
Is there any water coming from there when the system is losing pressure, boiler off?
Yes there is a white pipe outside of the house connected to boiler. I’ve put a milk bottle inside white pipe and can see 100 ml water.
When I checked with plumber he said that water meant to come through that white pipe and boiler stream converts into water
 

Stigster

Esteemed
Plumber
Yes there is a white pipe outside of the house connected to boiler. I’ve put a milk bottle inside white pipe and can see 100 ml water.
When I checked with plumber he said that water meant to come through that white pipe and boiler stream converts into water
Yes condensed water is supposed to be coming from there. It's only a problem if there is water coming through the condensate pipework when the boiler is not running. Just another possible escape route for leaking water.

If it only produces water whilst the boiler is running then the leak isn't coming through there.
 
Yes condensed water is supposed to be coming from there. It's only a problem if there is water coming through the condensate pipework when the boiler is not running. Just another possible escape route for leaking water.

If it only produces water whilst the boiler is running then the leak isn't coming through there.
Thank you very much.
I will put the bottle back and trace if water coming when system is ideal.

Any idea about magnet non return valve.
Would that need looking at.
I have attached picture of magnet filter
 

Stigster

Esteemed
Plumber
I think the magnetic filter setup is a red herring. If there's no leak visible there then it's not causing the problem. It's a sealed unit with no setup for automatic discharge of water or anything like that.

I believe the question about the non-return valve was asking about the filling loop, not the magnetic filter. The reason that was asked is that it is possible for the heating system water to get back into the water main without a non-return valve on the cold water main side.

Can you upload a picture of your filling loop setup?
 
Can the boiler be isolated from main system to see where you're losing pressure?
Many thanks sir
I have put bottle under the white dicharge pipe outside of home coming from the boiler.
I can see water in bottle when system is idea.
Does that mean the boiler leaking water.
If so where and what needs looking at to fix please
 
Many thanks sir
I have put bottle under the white dicharge pipe outside of home coming from the boiler.
I can see water in bottle when system is idea.
Does that mean the boiler leaking water.
If so where and what needs looking at to fix please
Hi. That is the condensate discharge pipe. When the boiler is running and in condensing mode you will see liquid flowing through that pipe, although it's a steady flow and not like water from a tap. Is the boiler running when you notice this discharge? How much have you collected in the bottle?
I haven't read all of the comments but Stigster has covered everything already I believe, which is why I asked if the boiler could be isolated from the rest of the system. ANY work involving removing the boiler cover requires a GSR though
 

Stigster

Esteemed
Plumber
Many thanks sir
I have put bottle under the white dicharge pipe outside of home coming from the boiler.
I can see water in bottle when system is idea.
Does that mean the boiler leaking water.
If so where and what needs looking at to fix please
If water continues to run from the condensate pipework when the boiler is pressurised but not running, then something is not right. Probably a leaking water jacket in the boiler. Not something you can be working on yourself.

Perform a test, fill the heating system until it shows 2 bar on the gauge then monitor the condensate discharge point with the boiler switched OFF. If you have water coming from the condensate discharge at that point you'll need a Registered Gas Engineer to come find the source of the leak within the boiler and take it from there.
 
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