Underfloor Heating Pressure Drop: Urlich Oil Oven, Expansion Tank, Thermostatic Mixing Valve

Hello.
I have a problem with the pressure drop in underfloor heating (water in a closed system is heated by an Urlich oil oven). For some time, the pressure drops in the expansion tank by virtually 1 bar per week (about one dash each day). A week ago, a plumber came to my place and he replaced the expansion tank with a new one, so it is not the tank's fault.

This problem has been going on for 2 months since the plumber replaced the thermostatic mixing valve for me. After a few days the pressure dropped to 0 and before I realized what had happened, the furnace walked so I suspect that from 1 day. Since then, the pressure drops and I have to allow water. To check, I turned off the inflow and outflow valve from the water distributor in the floor. Still, the pressure began to drop. So you can exclude floor installation. Only the section from the furnace, expansion tank to the distributor remains. I also looked at all the pipes and connections that are above the floor (some pipes are under the tiles) but I did not find any leakage.

I will also add that as the oven heats, the pressure increases by about 2 lines and there are no drops. After the furnace switches off, the pressure returns to its state before switching on and when the furnace does not work after about 5 hours, the pressure begins to drop. The longer the stove does not turn on, the more pressure falls.

Unfortunately, I am not a plumber myself and I rather do not want to do anything myself, but the plumber who made the installation for me and all the replacement lives 30 km from me and I have trouble contacting. Therefore, I am asking for advice on what else I can check or suggest to the plumber because I have already run out of ideas and the plumber also does not know what it can be because he bet on the expansion tank.

Thank you in advance for your help.

PS. I am sorry that I wrote so much but I wanted to describe the situation well.

mlpmlp11 wrote:

I will also add that as the oven heats, the pressure increases by about 2 lines and there are no drops. When the furnace switches off, the pressure returns to its state from before it switched on

In my opinion, before you even change anything, hold on a bit and watch the pressure gauge, because

mlpmlp11 wrote:

while the oven is not operating after about 5 hours, the pressure begins to drop. The longer the stove does not turn on, the more pressure falls.

And this is basically normal, because the temperature drops, and therefore the pressure also, unless it drops completely to 0, then it is no longer OK.

Or maybe water is escaping through the safety valve.

stanislaw1954 wrote:

And this is basically normal, because the temperature drops, and therefore the pressure also, unless it drops completely to 0, then it is no longer OK.

Only in this case that for 5 years (i.e. since I have this installation) the pressure dropped by 1 bar but only once a year and here it drops every week and it has been happening for 2 months.

mirrzo wrote:

Or maybe water is escaping through the safety valve.

I would also exclude a safety valve because I often watched the stove work or something was flying out of it. Also, there is no water on the floor just below it or anywhere in the area. The pipes are also dry and I didn't notice any steam coming out of them.

There is nothing else but to cut off the boiler with the valves and to make a pressure test on the rest of the installation. If there is a leak, then cutting off the subsequent floor circuits, find a faulty circuit and take a closer look at it: there are no leaks on the manifold, traces of patina on brass, brown stains, etc.
If there are no signs of leakage, the leakage may appear on the pipes in the floor. Beware of pex pipes us metrix tense after 10 years and are very fragile.

The friend is right. The safety valve may be damaged and thus spits out once and maintains water pressure once.
Put a transparent can on the safety valve, a bottle, or observe that the valve is not wet.
And replacing the collection vessel is just a strain on you. The vessel, if it has pressure (and this can be easily checked) will work without any problems.

pablos11111

pablos11111 wrote:

The safety valve may be damaged and thus spits out once and maintains water pressure once.

Read carefully with understanding.

mlpmlp11 wrote:

I would also exclude a safety valve because I often watched the stove work or something was flying out of it. Also, there is no water on the floor just below it or anywhere in the area. The pipes are also dry and I didn't notice any steam coming out of them.

Only pressure test of the installation (floor), as described by Kol. Andrzej Ł.

andrzej lukaszewicz wrote:

There is nothing else but to cut off the boiler with the valves and to make a pressure test on the rest of the installation. If there is a leak, then cutting off the subsequent floor circuits, find a faulty circuit and take a closer look at it: there are no leaks on the manifold, traces of patina on brass, brown stains, etc.
If there are no signs of leakage, the leakage may appear on the pipes in the floor.

Ok I will try to do that. I'll let you know if I can find something or not ...

Interestingly, on Sunday evening the pressure dropped to 1bar but I could not finish the water and the stove turned on. The pressure suddenly jumped to 1.8 and it remained so until Monday morning. Then I decided that I would allow water lightly just in case (I had to go to work and did not want to worry). I admitted to 1.9 bar, which is about 100 ml and it is still used today. There are no drops, regardless of whether the oven is working or not. (although it often turns on every 5 hours. It is -6 degrees outside). In the old tank, as soon as the stove turned off (well after 1 hour), the pressure always dropped by 2 lines.

I also had a signal from a customer that the pressure from the heating system was falling.
Interestingly, as the installation was warm, the pressure did not drop. As it cooled down, the pressure dropped to 0.
It turned out that the reason was a damaged ball valve.

It often happens that when you close you open the valve handle, there is a slight leakage from the valve stem.

mirrzo wrote:

Or maybe the water is escaping through the safety valve.

Hello,

Thank you for all your comments because I have a similar problem as mlpmlp11 in the central heating installation [underfloor heating] and the Vitodens gas boiler.
Water pressure drops of about 0.1 / 0.2 bar per day on the boiler pressure gauge.
It turned out as above.
Boiler about 10 years.
After removing the housing, the leak from the safety valve is clearly visible:

Greetings

takitamelektron wrote:

After removing the housing, the leak from the safety valve is clearly visible:

This in the picture is a vent.

piracik wrote:

takitamelektron wrote:

After removing the housing, the leak from the safety valve is clearly visible:

This in the picture is a vent.

A vent, indeed.
Nevertheless, thanks to this thread, it was possible to direct the search for a leak towards the furnace and not the central heating installation.
Thanks again.