Underfloor heating on the upper floor - one room always remains too cold

Hello everyone!

I am at my wit’s end. I just can’t get the children’s room above 20.5 degrees Celsius, while all the other rooms on the upper floor reach 21.5 to 22.0 degrees under the same settings. The affected room also feels noticeably “cool.” I increased the flow rate a bit without success (+0.3 degrees). In the meantime, the valve is 95% open but without any change in room temperature. Thermal imaging camera showed nothing unusual, no cold spots. Checked all window seals, also unremarkable. Checked photos from the installation of the underfloor heating, no abnormalities. Hydraulic balancing has been done twice to rule out errors. Two heating circuits of identical length run through the 17 sqm room. Pipe spacing is 10 cm. Flow temperature at 5 degrees outside temperature is 27 degrees. Heating curve is at 0.35 and thus at 0 degrees outside temperature about 28.3 degrees flow temperature. We have 22.2 degrees on the ground floor, so the flow temperature can’t be the problem. Controlled ventilation was turned off for 24 hours, no change noticed. Carpet removed for 24 hours, no change. Only a small wardrobe is on the floor, the bed is a loft bed and does not affect the underfloor heating. I don’t understand why the room stays noticeably cooler than the room next door (exactly the same conditions). Do you have any other idea where the problem could be? I don’t want to increase the flow temperature because of the 17 sqm, if there is no reason for it in the rest of the 140 sqm.

First of all, check whether the circuits and thermostats have not been swapped. This happens more often than you think. Therefore, close all other circuits on the floor and then see if it gets properly warm. After that, carry out the thermal balancing instead of the hydraulic balancing. How is the flow rate in the room? How is it in comparable rooms? Two circuits and 10cm installation spacing sounds pretty good at first.

First, check whether the circuits and thermostats have not been swapped. This happens more often than you think. Therefore, close all other circuits on the floor and then see if it gets properly warm. After that, instead of hydraulic balancing, perform thermal balancing. What is the flow rate in that room? How is it in comparable rooms? Two circuits and 10cm installation spacing sounds great at first.

I was already able to exclude swapped circuits by checking the photos from the installation. The flow rate is identical (2.8L/min out of max. 3L/min) to that of the other rooms since I meticulously paid attention to the length of each heating circuit during installation. I basically control the temperatures only via the supply temperature. Throttling a lot at the individual regulators makes little sense to me anyway. In the bathroom, we have an additional heater for extreme outside temperatures. We have also already done the thermal balancing. That’s why I’m at my wit’s end. The fact that it works to reach the target temperature throughout the whole house but just won’t work in this one room is driving me crazy.

I was already able to rule out the swapped circuits by checking the photos during installation.

I would really check that again.

The flow rate is identical (2.8L/min of max. 3L/min) to that of the other rooms as I was meticulous about the length of each heating circuit during installation.

Please post a picture of the distribution box.

We have also already done the hydraulic balancing.

Here I would say: obviously not.
Hydraulic balancing does not mean that the flow rates are the same, but that the temperatures are as desired.

Please insert the floor plan here, that is, the layout.

Remove the valve and control the flow only via the tacosetter.

Then please provide a picture of the distributor, maybe there is a bypass installed there that regulates too early.