Low Return Temperature in Defro Comfort Eco 15kw Oven: Struggling with ±37°C vs. 68°C Set

Hello to all forum members. I would like to present my problem with the low return rate from the installation to the furnace being at + -37 ° C at the set on the furnace 68 ° C. Stove for eco-pea coal Defro comfort eco 15kw with controller k1pv2 with pid works in a machine with weather sensor and 4d motor. When the floor circuit is running and every return temperature is very low. The situation changes a few degrees higher if the dhw pump starts to work. Like the return from 4d was to protect my return from too low a temperature and it does not. The cross-section of the return pipe from 4d is 1 1/4 "and supposedly had a gravitational effect. It works but only in the summer mode, and when the pump starts from the floor, the return flies to the neck. I think that this gravity has no breakthrough and mix with water pushed by pumps. On another forum they advised me to put on the clutch only that I would have to rework a very current installation and it is expensive. Maybe I can do something about my bolko and maybe the stove will start working steadily and not chasing and picking peas to maintain the set temperature I thought to give a circulation pump on return from 4d with bypass because there is probably no such a thick pipe. Below is the diagram of my installation.

It should look like the first diagram. In my opinion, the second scheme is also legitimate (and I may be wrong). Then I would not have much change, but I do not know if I can put a pump on the return because I have 1 1/4 "there. Unless it can be without this pump by the stove.

An installer who supposedly knew how to do it properly installed this installation but he will not improve it because he is permanently in another country. Now 4d controls the motor from the weather. I have thermostats but they are not fitted because it is an actuator. I would like to find out if any of the following schemes will solve my problem with flooding the boiler with cold water from the return, and thus eventually this stove will work steadily and not all the time chasing to the set temperature. Maybe some of you use such solutions and know that it works or even at home.

So you can, for example, set your hot water pump as circulating?

Gentlemen, I still have a question. At auction there are available hydraulic couplings with a manifold made privately which are much cheaper than those from the store. Is it worth considering them at all?