ᐅ Refilling underfloor heating system

Hello everyone,

I have to admit that I haven’t really taken care of our 8-year-old heating system (in a newly built single-family house). Last winter, I noticed that one of the two heating circuits in the living room wasn’t getting properly warm. I thought, okay, I’ll deal with it in the summer ^^

Now I’m 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 in 8 years... I had assumed it’s a closed system... we never had freezing issues... The chimney sweep measures everything yearly and never had any complaints...

I’ve attached a photo. I would proceed as follows:

1) Close both ball valves
2) Close all the small black dials at the top
3) Connect the water supply to the connection at the red ball valve
4) Attach a hose to the connection at the blue valve and place the other end in a large bucket
5) Slowly open the water tap and then gradually open each valve at the top slightly, one by one, until only water (and no air) comes out into the bucket...

I have three questions about this:

1. Question: A friend of mine has to screw caps onto the valves on top that he was given. I didn’t receive any caps. Is it enough if I just close the small black dials by hand?

2. Question: The hose for filling should be air-free... Is it sufficient to run water through it completely until a steady, clean stream comes out before briefly bending the hose to connect it?

3. Question: Do I need to remove the actuators (motorized valves) on the lower row, or can they stay on?

Thanks for your tips