intermittent pressure loss in heating system

mrblack

I have noticed that the pressure drops in our pressurized heating system from 2 bar to almost zero and have refilled it a few times already over past year or so. So on Saturday I decided to tackle the issue.

I filled the system from zero back to 2 bar and bled all the rads including towel rads, pumped up the expansion vessel to 2 bar and then refilled it again to take up the drop from the bleeding. There is about 35 rads in all -so it took a while. Then I watched the guage over next 3-4 hours and the pressure held firm at 2 bar all day. Then I turned on the oil burner and again the pressure stayed steady at 2 bar for the next few hours.

I thought that the leak had resolved somehow and congratulated myself on my brilliance.

Unfortunately, last evening I noticed that the pressure had dropped back to 0.25bar. I did notice that the heating was on for a long time (maybe 2-3 hours) on Monday & Tuesday and am thinking that maybe the pressure loss only happens when the system gets very hot for a long time. Or perhaps its the DHW coil as there are definitely no leaks in the pipework (since the pressure never dropped while the heating was off)

If I turn off the balancing valve so that the DHW cylinder coil wont heat the cylinder and then repressurize the system- then if no leaks occur over a few days then I can be sure that the leak must only be in the coil. Or if there is a leak then I can be sure that the leak must be in some pressure valve somewhere in the pipework within the hot air press or perhaps in the boilerhouse.

Does this logic make sense? and what does a PRV or AAV look like?

Appreciate any help and advice. My aim is to be in a position to point plumber to the source of the problem and avoid wasted time and cost of him having to investigate the issue.

Thanks

MrBlack

K.Flyer

Where is the vessel located and what type of heating system do you have, gas or oil?
2 bar cold is far to high on a heating system and 2 bar in the vessel is also too much.
Vessels should only be pumped when its possible for the air pressure to freely expel any water contained in the vessel, and should not be pump into a "closed" sealed system. Otherwise you can get incorrect pressure readings.

mrblack

K.Flyer wrote: »

Where is the vessel located and what type of heating system do you have, gas or oil?
2 bar cold is far to high on a heating system and 2 bar in the vessel is also too much.
Vessels should only be pumped when its possible for the air pressure to freely expel any water contained in the vessel, and should not be pump into a "closed" sealed system. Otherwise you can get incorrect pressure readings.

Hi K.Flyer, its a kerosene system with a Firebird 58kw boiler and riello burner I think.

I used the 2 bar as the expansion vessel said 1.5-2.5 bar max.
There is guite a head of height the system has to reach as the boiler is about 8 metres from the house, and is a bit below the house and the rads also go up to the attic which we have converted. So the volume in the system is quite big-hence the 58kw boiler. When the pressure was low last week the rads gurgled a lot and the top of the house didn't get much heat at all. Repressuring on Saturday to 2 bar fixed those two issues completely, albeit temporarily.

Wearb

Prv. https://www.google.ie/search?q=prv+valve&client=safari&hl=en-gb&prmd=ivn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjKkaXCovjPAhVkAsAKHSHWDVsQ_AUICCgB&biw=320&bih=372#imgrc=eBAzW3-0jS640M%3A

What size is vessel? Pic?

Turning off balancing valve only stops flow. It doesn't isolate water from coil.

How high is highest rad above vessel?

mrblack

What size is vessel? Pic?
The expansion vessel I presume you mean. Will put up a picture of it up later when I get home.

Turning off balancing valve only stops flow. It doesn't isolate water from coil.

I am not sure I understand what you mean on this point. If I stop the flow of heated water going through the coil in the DHW cylinder, won't that allow me to exclude the coil as the leak if the leak still occurs, or if the leak doesn't occur then the coil must be the site of the leak.

How high is highest rad above vessel?
About 8.5 meters.

Mrblack

Wearb

mrblack wrote: »

What size is vessel? Pic?
The expansion vessel I presume you mean. Will put up a picture of it up later when I get home.

Turning off balancing valve only stops flow. It doesn't isolate water from coil.

I am not sure I understand what you mean on this point. If I stop the flow of heated water going through the coil in the DHW cylinder, won't that allow me to exclude the coil as the leak if the leak still occurs, or if the leak doesn't occur then the coil must be the site of the leak.

No. The coil is on a loop and the valve only stops one end of this loop.

How high is highest rad above vessel?
About 8.5 meters.

1.5 Bar should be enough at vessel (yes expansion vessel). How high is the vessel above the burner?

Mrblack

.

mrblack

Hello Wearb,

The expansion vessel is about a foot above the boiler.

Re the coil-is it not possible to totally cut off heating water from entering the coil? I could instead try the opposite approach and power off the motorized valves which allow heating water to heat the ground and upstairs zones. Then if the leaks occurred while the heating was only going to the coil in the cylinder (and the 4 towel rads) - at least I could exclude most of the pipe work in the two off zones from being the site of the leak.

I am beginning to understand why leaks are so difficult to find>:(

Wearb

Proper way to test is to drain down, isolate the circuit being tested and pressure test. I think you will need a plumber to test your system.