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Trying to get my head around this system in our cafe. It's the relationship between the circulating pump and the ?bypass (above the red knob on the right) that is not making sense to me.
It just seems like the circulating pump is dragging the cold water around and around through the loops. It's doesn't look like other manifolds I've googled...
What you have there is a standard manifold, plus a temperature-controlled recirculating pump (which is not the main pump!) and a hot-to-cold bypass line.
Try closing the bypass valve. The picture isn't too good, but I assume those are all temperature gauges, so the only warm water flows through the bypass at the moment.
Yes, there's another pump back in the main line from the boiler.
With the bypass valve closed, the hot water doesn't seem to circulate at all - either down the bypass or through the loops.
And, the thermostat on the circulating pump there switches it off below whatever temp you set. Once switched off, then the top rail starts to heat (implying that got water is now going into the loops). So strange , I just can't get my head around how it's 'supposed' to work, let alone if it's actually working properly.
Realistically, at this point you call s professional and get it checked out and explained to you.
I've tried. We're rural and tradies just don't want to know.
I'm not necessarily familiar with subfloor heating systems but I'll give it a shot. I found this video that helped sort some of it out.
https://youtu.be/OSJkjcTHVLE?si=aGyvO6ue3Ng0FT9I
From what I can tell it looks like the hot water comes in from the top line and heads into the manifold but also down to the mixing/regulating valve on the bottom line. After the water runs through the system it comes out to the return line and back out to the heating system.
My first thought is to try closing the blue valve on the return a bit and give it a minute. My thought process is that reducing the cold/out flow will help the circulating pump pull the water from the mixing valve. You could also try messing with the regulator to see if the temperature changes when you adjust it.
The red knob is a thermostat. Hot water will flow in their, coming from the gas furnace most likely. The floor heating can't handle too hot water, so it's mixed with the circulating water coming from the top rail. The tube going from the thermostat to the top rail probably only has a thermometer in it, to measure the temperature of the returning water. If it's too cold, more hot water can be mixed in.
The pump you see is circulating water through the floor heating. The gas furnace will have another pump, distributing hot water through the building.
It seems to make no sense. The top rail is hot and the water should flow through the circuits back to the cold rail on the bottom. The pump should be in-line and not across the rails. The pipe on the right between the top and bottom rails would also seem to be defeating the purpose of the two rails, allowing water to flow from hot to cold directly. It looks like a rebuild is in order.
There is another pump that is in inline with the heater. This pump is needed to mix the hot water from the heater with circulating water from the floor heating, to have an acceptable temperature for the floor. Water directly from the heater can be too hot for floor heating.
There is something wrong with the setup if the boiler is putting out temperatures too hot for the floor heating, e.g. a radiator circuit is being used for both radiators and underfloor circuits.
That is a typical setup for heating here in the Netherlands, I have it in my house. OP is in Germany, so probably not too different.
Edit: OP is not in Germany, but there are German stickers in the picture