No Water or Air When Bleeding Radiators—Possible Causes and Next Steps?

Hello . I have a problem with the radiators at home. Recently I found out that there is air in them and they do not heat properly, i.e. they are cold at the top, which makes it cool in the house. I found instructions on how to bleed them (I don't know anything about it at all). I bled them by unscrewing the screws with a flat screwdriver in the upper corner of the radiator. In two of them you could hear the air escaping and water started flowing and now they are fully heated. However, in the next two, after completely unscrewing the screws, neither air nor a drop of water came out, and after turning on the heating, you can clearly hear the sound of water flowing inside. What else can I do? Is it possible that the vent hole is clogged inside? It seems to me that no one in this apartment has vented the radiators for a long time. Thanks for the help in advance

Maybe you just need to top up the water in the installation

Just like the thing with circulation pressures ??

This hole in the vent may be muddy or clogged with scale. It is better not to try to open the vent under pressure, but if there is a valve on the return, you can turn off the supply and return of the given radiator and then, for example, completely unscrew the screw closing the vent (if it is a manual vent) and clean the hole with some wire, or simply replace the vent . In general, when bleeding air, you should only loosen the screws (unscrew them only enough to let the air escape, usually 1/2 turn is enough), and not unscrew them completely, because if they were already on the last fragments of the thread, the pressure could then push them out of the breather and it would geyser in the apartment.

While bleeding other radiators, I noticed that the more I unscrew the screw, the stronger the water flows, but I can't say it's a geyser, rather a dripping, but in two radiators, after completely unscrewing the screw, nothing comes out at all. Unfortunately, I don't know how to check the pressure or how to check whether you need to add water and how to add it. I have always had a coal stove at home, and now in the recently rented apartment we have gas heating and operating it is black magic to me.

Do you have your own cauldron? You should have a pressure gauge on it

there is a Junkers Bosch gas furnace in the basement

this is what the stove looks like

Pump the pressure, it's almost 0
There is no pressure at the top of these radiators, even though it shows a little, it is only a column of water.
Allow approximately 1-1.5. Bleed and check again.

But how to do it, I have no idea

Is there no valve in the furnace for filling the installation and the furnace?

There are several different valves under the stove, but it is not written what they are for and I don't want to spoil anything. I think the best solution will be to call a service technician. Unfortunately, it will probably cost a lot, but if it is to reduce gas bills and make it warmer, it has to be done.

Take a look at the stove's instructions.
Mine clearly describes which one is used for what.

Unfortunately, I don't have the manual and there is no model on the stove to find instructions for it, so I think I'll leave it to the professionals

Hmm, I have valves under the stove: admitting water, closing the entrance, closing the outlet, gas.
The gas valve is yellow.
Blue water release.
Closing the inlet and outlet are standard ball valves.

Closing the entrance or exit when the stove is turned off should not spoil anything.
Admitting water should be visible on the manometer (pressure increase), but it must be done slowly so as not to create air in the system (that's what I read in the manual of my furnace) and not to activate the safety valve (if the admission valve suddenly opens).

Another issue is the pressure drop in the installation, it had to come from somewhere...

Show more photos of this stove - especially the bottom, where there is a water connection, drains to the radiators, water inlets, water outlets, etc. When water is admitted, the ball valve will have a blue color or a red handle, when you unscrew it, you should hear something and the pressure will increase on the manometer. It may be a valve with an inclined filter that protects the system against garbage in the water. The directions of water inlet and outlet may be marked on the furnace casing on the furnace parts. Ask the owner if you are renting an apartment from him, he should know, maybe there is this type of furnace on a frame or casing somewhere? .

Thank you to everyone who tried to help me solve my problem. Yesterday, a specialist from Junkers arrived, added water, performed maintenance on the furnace and now everything should be fine. Regards