ᐅ Underfloor heating on the first floor is no longer working.

At least you should have installed the Tacos.

But never mind, just set up a thermostat and open the blue valve, of course checking its function beforehand.

No, you don’t see that; I’m not talking about the missing taco setters.
There are manifolds that regulate the flow on the return line; these often have a square adjuster with a scale visible from above.

T_im_Norden schrieb:
No, you don’t see it,

Somewhere on page 1 or 2 he had pictures, but I also thought he had some because he posted the distribution board.

On page 1, you can see the three manifolds as they are. An independent heating contractor assembled them like this 19 years ago. Why or how, nobody knows. There is no scale on the manifold itself.

qwertzuiop schrieb:

small update, I have now vented the floor 6 times

Oh yes! Venting! A step often forgotten in the age of underfloor heating. Nowadays, automatic air vents are usually installed, and that’s the end of it. But since you have an older system, venting underfloor heating can be a bit more complicated than radiators, so I assume you still have air in the system, which is why the rooms aren’t heating properly. Of course, there could also be other issues causing noises.

qwertzuiop schrieb:

could it also be that the pump no longer produces enough pressure?

Yes, of course. After 19 years, the pump can definitely stop working properly and only deliver limited performance.

qwertzuiop schrieb:

or that the valve inserts are sticking, see picture 1, I noticed that some move freely when pressing the pin in, and some are stuck tight. I’ve also sprayed a little oil on them to help them move.

Another common issue. Valves, especially if they aren’t operated from time to time (which seems to be your case), can seize up or rust. Replacement is usually the only solution. Also, it’s unclear what kind of water you have in the system and where the air is coming from, all of which is bad for operation.

qwertzuiop schrieb:

Or is it because we have different blue caps since some were broken, where can you get new ones anyway? I already asked if they can be bought separately but apparently they only come together with a new manifold, these blue caps.

The blue caps serve only to press down the pin and keep the heating zone open. Color and shape don’t really matter, and yes, they tend to break after some time—it’s just plastic.

Try searching for “manual radiator valve” (Handversteller Heizkörper). You’ll find something suitable, maybe a different design but with the same function. The standard size is 30x1.5, which should fit.

From the pictures, it looks like the flow might be adjusted using those caps (which would be unusual, but who knows what exactly was done 19 years ago). Make sure to carefully note the number of turns before and after removing them, so you can set the new ones the same way. This is just a guess, though. There might be regular square adjusting valves underneath the brass caps.

qwertzuiop schrieb:

there is no scale on the manifold itself

You don’t really need one. These scales, and devices like TacoSetters, are helpful but basically not necessary.

A small update: after bleeding the system about 10 times and refilling water, oiling and loosening the valve inserts’ knobs, and replacing the blue caps, everything is working again. I had originally thought this was part of regular maintenance—otherwise, why would they do it? Instead, every year they just stick their stamp on the heating system to show they were there.

Now I just need 5 new blue replacement caps. Does anyone know where I can find these? I already asked a seller who said they only sell them together with a new corresponding heating manifold circuit.