Refill underfloor heating

Hello everyone,

I have to admit that I haven't really taken care of our 8-year-old heating system (in the newly built single-family house). Last winter I noticed that one of the 2 heating circuits in the living room did not get properly warm. I thought, ok, I'll take care of it in the summer ^^

Now I am standing in front of the system and see on the gas boiler (Junkers) that the pressure is almost at 0... I haven’t added any water for 8 years... until now, I assumed that it’s a closed system... we never had freezing... The chimney sweep measures everything yearly, and he never found any issues...

I attached a photo. I would proceed as follows:

1) Close both ball valves
2) Close all the small black knobs at the top
3) Attach the water supply to the connection at the red ball valve
4) Attach the hose to the connection at the blue valve and hang it into a large bucket
5) Slowly open the water tap and then gradually open each valve on top slightly one at a time until only water (no air) comes out into the bucket...

However, I have three questions about this:

1. Question: a friend of mine has to screw caps onto the valves on top which he received with it. I didn’t get any caps. Is it enough if I just close the small black knobs by hand?

2. Question: the hose for refilling should be air-free... Is it enough if I run water through it completely before connecting it to the system until a clean stream comes out and then briefly kink the hose to connect it?

3. Question: do I have to remove the actuators on the lower row, or can they stay on?

Thanks for your tips

Don’t you have a way to refill water directly at your heater? Otherwise, I can’t answer your questions. I don’t have underfloor heating. But with the two hoses, it sounds very strange. Because that way you would basically be flushing the system.

Is flushing and filling not the same to remove any air from the heating circuits?

No, actually not. The heating system is operated with overpressure. For example, 1.5 bar above atmospheric pressure. During flushing, you would never achieve an overpressure. For venting, the small white valves above the hose connections are there. You open these and the air comes out. As soon as water comes out, close them again. Of course, this only works if there is sufficient overpressure.

Oh okay... since I currently have no pressure on it, it is therefore sufficient to just refill with water until the pressure is correct... then bleed it and if necessary, refill a little water again?

The question is of course why there is no pressure anymore? Or how much is optimal.