The problem with pressure during the operation of the pump TSRm-158A

Hello! The story is like that. There is a pump ТСРм-158А and an electronic pressure controller EPS-16 manufactured by “Pumps plus equipment”, Kharkov. The controller stands about 2.5 m above the pump. The suction and pressure pipe to the controller are plastic 50 mm. The home wiring is also a 20 mm plastic pipe. highest point 2.5 m above the controller. According to the instructions and description of the controller, it must ensure the operation of the water supply system in the house as a full-fledged household pump station. When using cold water, this is what happens.

The pump generates a shut-off pressure of about 2.2 MPa, switching on occurs at a pressure of about 1.1 MPa. The pump turns on and off, there are no arbitrary inclusions indicating a leak in the system, and there are no leaks to the eye at the joints of the pipelines. However, when the Delimano-type instantaneous water heater is turned on after a short time of using it (about 3 minutes), the indicator light on the dry-running system will light on the controller and it will turn off the pump. If the water heater shut off earlier, then as the system operates until the shutdown pressure is reached, the same story repeats. Restarting the position system does not change. This continues until you open the tap to drain cold water at any other point.

After a little, up to 1 liter. draining water from it all comes back to normal. On the advice of the manufacturer’s representative, I tried to change the switching pressure with an adjusting screw - it didn’t help, I bought a hydraulic accumulator and mounted it in the system (I installed it both before and after the controller), but it didn’t change anything either. Representatives of the Kiev service center of the manufacturer say that my pump does not provide enough pressure (with their more "advanced" pump, when checking the controller shutdown pressure was about 4 MPa.) They did not consider it necessary to check the operation with the aforementioned water heater, because everything is clear to them (buy a new pump from us and you will be happy).

Tell me, please, what to do? Spit on expensive advanced electronics and install a typical mechanical relay, or is there any reason I can’t think of? Thanks in advance for your reply.