How does my heating system with solar thermal work?

Hello everyone,

our heating system consumed about 8700 kWh of natural gas between 12/16 and 06/17, although the house is still being renovated and unoccupied. In other words, all radiators were only set to frost protection and no domestic hot water was used either.

The system was installed in 12/15 by the previous owners and essentially consists of:

[*]Viessmann Vitodens 200 gas condensing wall unit 19 kW
[*]Austria Email KWS 800 combined stratified storage tank
[*]Solar flat collectors 9.36 m²
[*]ESR 31 solar controller
[*]Delphis solar station FV 70 (with Grundfos circulation pump in the supply line)

In summer, I noticed that the line from the solar collector (supply) was only really hot up to the pump, and the return line was practically cold. From this, I already concluded that the pump is not running. At the same time, the controller shows 999°C for the temperature sensor mounted at the top of the collector, which according to the technician is the upper limit displayed when no plausible value is measured.

The temperature sensor (it is a PT1000) was checked successfully, which led the technician to conclude that the controller itself must be defective (in his opinion, the pump itself was operable...).
So, a new controller was ordered, which I am still waiting for as of today, but that is another matter...

Now, since the cold season is approaching, we have temporarily installed some radiators to heat the construction site a bit and of course primarily to ensure frost protection.
I was able to reduce natural gas consumption by lowering the set temperature for domestic hot water to 10°C, but I would say the consumption is still quite high (since Saturday, so in 4 days, ~30 m³... :O).
Is it therefore conceivable that due to the defective controller the 800 liters of water in the solar thermal system are being kept warm using natural gas and normally the ESR 31, depending on whether heat from the roof is available or not, activates a heat exchanger between the domestic hot water tank and the solar thermal water system or not, and that this is currently always open in our system or something similar?
Maybe someone layman can explain to me how a combined stratified storage tank works or is constructed?!

Thank you very much in advance!

Regards

PS: The heating technician is hard to reach; unfortunately, I have to work with him because it is, of course, a warranty case. Once this problem is solved, he will certainly not touch our heating system again... -.-

Why do you have to work with him? Set a written deadline and then hire someone else. And send him the invoice. Preferably do that with a lawyer and that's it.

First, I would completely turn off the hot water preparation, if possible. Then you can see if the consumption is noticeably due to that.

A combined stratified storage tank is, to my knowledge, designed so that the temperature is not the same throughout the entire water tank. At the top it can therefore be 50 degrees, and at the bottom only 30. Exactly how, a specialist must explain that to you in more detail.

First, I would completely turn off the domestic hot water production, if possible. Then you can see if the consumption is noticeably due to that.

The Vitodens 200 has only 3 operating programs: "Heating and hot water," "Hot water only," and "Shutdown mode." Unfortunately, there is no "Heating only" program. Feedback from Viessmann regarding this, which I have already done, is to lower the setpoint temperature of the domestic water to 10°C. €dith adds: If you shut off the fresh water, the system goes into fault mode, so that does not work either...

To my knowledge, a combined stratified storage tank is designed so that the entire water tank does not have the same temperature. Therefore, the top can be at 50 degrees, and the bottom only 30. Exactly how that works should be explained to you in more detail by a professional.

Thank you very much for your explanation. If someone can/would like to explain it more precisely, I would be very grateful! Above all, I would be interested in how it is prevented that in winter, when no/almost no heat comes from the roof, heat from the domestic hot water is lost towards the solar thermal system? (Because otherwise, the system would probably be pointless...)

Towards the roof, nothing works... that's a one-way street. So either heat from the roof into the storage or nothing at all...

Heat definitely does not rise upwards. This is also clearly visible by the fact that snow remains on the panels (until it slides off) and ice can form. They are therefore cold in winter.