Hydraulic short circuit? Return flow of radiator upstairs warmer than supply flow

Good evening everyone,

In January of this year, an Arotherm Plus was installed at our place, and in this process, the fixed-value control set of the underfloor heating was replaced (the actuator was defective, and spare parts were no longer available). On the ground floor, there is underfloor heating, and on the upper floor, radiators (which were replaced with type 33 during the conversion). The installed fixed-value control set from the heating installer did not work at all and was replaced with a purmo tempco fix 3 eco fixed-value control set. Unfortunately, it is still the case that the return flow of the upper floor circuit is warmer than the flow. The return flow of the upper floor runs together with the return flow of the underfloor heating (I hope this can be seen in the photo), and this seems to be where the problem lies. The pressure from the underfloor heating seems to be too high, so it pushes into the return flow of the upper floor. For me, there are two solution approaches: 1. Separation of the two heating circuits, at least the return flow up to directly before the heat pump. The flow temperature is the same, however. 2. Integration of the return flow of the upper floor between the return flow of the underfloor heating and the fixed-value control set, so that it uses both return flows for mixing and sends the rest back to the heat pump in one pipe. The problem here is the available space and the connection.

What do you think of these possibilities, are there perhaps other ideas, and is this a defect that the heating installer must fix?

Thank you in advance and have a nice evening!

Sounds very strange. How did you measure that? What is the actual problem? Does it not get warm? Is the consumption too high? Do you have a drawing of the hydraulics or can you make one?

Good evening,

I measured it with two thermostats directly on the pipes (they can also be seen in the photo: supply just under 29 degrees, return about 30.5). The actual problem is the consumption (COP) or frequent cycling at temperatures where it should simply run continuously (COP 2.9 at 2 degrees outdoor temperature, according to Vaillant it should be over 4). It's getting warm by now, I've managed that so far, probably I could lower the supply temperature even more once the problem is fixed. I can gladly draw up a diagram of the hydraulics tomorrow and upload it.

Good morning,

attached is a simple drawing and a photo along with flow directions. The problem area is the yellow circle, here the pressure from the return flow of the underfloor heating seems to be so high that it pushes into the return flow of the upper floor. The hydraulics of the house do not seem to work well with the current conditions, as the system was simply set up differently before the renovation. I have attached a photo of the previous construction, in which the UWP of the underfloor heating drew suction from the return flow of the underfloor heating, so the pressure in the system only arose in the supply line and not as it is now, also in the return line. I hope this is understandable so far?! ,-)

We need the complete hydraulics. Not just the small section. Normally, the air-water heat pump would directly push into the heating circuits with the integrated water pump. Here I see an extra pump in an "interesting" spot. Why is that? Are there buffers, etc.? Is it possible that the thermometers are simply inaccurate? What does the thermostat do in the distributor?

Good evening,
tomorrow I will draw a complete hydraulic plan, I have just never done something like this before,
brief summary of the setup: downstairs 5 rooms with underfloor heating, upstairs 4 rooms with radiators, the distribution can be seen in the photo, in front of it is only the air-to-water heat pump. ,-)
It is correct that there is a circulation pump installed in the air-to-water heat pump (Arotherm Plus 75/6 with Unitower Plus 190). The additional pump was installed during the heating system conversion due to a defect in the old system (red Grundfos circulation pump / mixing controller at the plastic housing was broken). As a layperson, I actually assumed that the second circulation pump is absolutely necessary for the underfloor heating. Thinking about it carefully now, it is quite silly, since nothing has to/should be mixed because I run the same flow temperature in the underfloor heating and the radiators (which were replaced with type 33 for a lower flow temperature).
There is a 35-liter buffer in the return line in the air-to-water heat pump, which the heating engineer insisted on; the bypass valve is closed as much as possible, ERR were removed, and a hydraulic balancing was performed via the flow rate.
The thermostats were actually taken over from the old system for my own understanding, but the values were plausible since the return temperature to the radiators upstairs was warmer than the flow temperature. Of course, there is still the possibility that the values are inaccurate; I will get myself an IR thermometer to check this more precisely.