Freshwater station with strongly fluctuating hot water temperature

Hello,

I have installed a fresh water station (Buderus FS 2) on a buffer tank (Buderus PNR750-C).

Unfortunately, the temperature of the hot water produced by the fresh water station fluctuates greatly!
Attached is a picture showing the enormous fluctuations.
The fresh water station produces hot water (at a buffer tank supply temperature of 70 degrees) sometimes at 62 degrees Celsius and sometimes down to about 25 degrees Celsius.
Showering is a nightmare when the hot water temperature uncontrollably swings up and down by up to 40 degrees.

Possible causes such as too low a buffer tank temperature can be ruled out (it is consistently high at about 70 degrees).
The draw-off rate of 8 liters/min is also well below the performance of the Buderus FS 2 of 22 liters/min.
The temperature of the incoming cold water is also constant. There were no other simultaneous draw-offs either.
The primary pump in the fresh water station also shows no error.

(The entire system consists of a Buderus Logaplus package S94 together with the Logaplus package K33/2)

What else could it be? I look forward to all ideas. As it fluctuates now, the Buderus fresh water station is unfortunately totally unusable :-(

Best regards!

At which point was the water taken for the test? Since when has the problem existed? Is a circulation installed and active? A defective valve with thermostat can be the cause. It does not even have to be the one from which water is taken, but any other. The thermostat uncontrollably allows cold water into the hot water line.

Hot water produced by the fresh water station fluctuates very strongly!
Attached is a picture that shows the enormous fluctuations.
The fresh water station produces hot water (with a storage buffer flow temperature of 70 degrees) from 62 degrees Celsius down to about 25 degrees Celsius at times.
Showering is a nightmare with this when the hot water te

At what point was the water taken for the test?
Since when has the problem existed?
Is a circulation installed and active?

A defective fitting with a thermostat can be the cause.
It does not even have to be the one where water is drawn, but any other one.
The thermostat then lets cold water uncontrollably into the hot water line.

Hello, many thanks for the questions and ideas!

The measurement of the produced hot water as well as the storage buffer temperature is done directly via the sensors installed on the fresh water station and was read out via the Buderus control panel RC320. Additionally, the hot water temperature was measured at the tap point and validated accordingly (matches the sensor measurements).
A thermostatic fitting at the tap point is not present; the heating system is about 1.5 months old. The problem has existed since the system was commissioned. Since the system is brand new, a malfunction of the fresh water station or the storage due to scaling can at least be ruled out. The hot water circulation was deactivated for the test to avoid interference with the measurement.
The strongly measured fluctuations of the hot water temperature produced by the fresh water station can therefore be seen directly at the hot water outlet of the fresh water station.

My question is also whether it is really possible that a fresh water station, despite more than sufficient sizing, a high storage buffer flow temperature, and constant draw-off speed, may have such fluctuations in performance. I consider +/- 30 degrees to be unacceptable. I also can’t imagine that all fresh water stations fluctuate like this, can they?

Hello,

an update:

The cause of the fluctuating hot water temperatures at the fresh water was apparently air that had accumulated in the storage buffer.

Solution: Release air from the storage buffer (via the vent either on the storage buffer) and refill water via the refill station.
Of course, keep an eye on the maximum pressure using the pressure gauge.

Hope it helps one or the other next time!

Best regards