ᐅ Storage heats collector

Hello everyone,

Last year, my wife and I bought a house. It’s not a new build but an older detached house that has been modernized several times over the years.
We have a combination boiler that runs on wood and pellets. There is also a solar thermal system on the roof, but it was only connected this year. Apparently, there were problems with the system and the heating technician was unavailable for a long time.
The system has been working very well all summer so far. I haven’t had to use any additional heating. In the past, there were a few days with very gloomy and rainy weather, so I had to add heat after about three days.
During this time, I noticed that my heating energy was being transferred to the solar collector. Of course, I discussed my suspicion with the installer, but he said that if the pump is off, no circulation is possible.
Over the weekend, my neighbor and I inspected the piping system and discovered a shut-off valve. Yesterday, I ran an experiment using this valve, which went as follows:

Yesterday at 9:30 PM, without any sunlight, the temperature on the collector’s upper sensor was 73°C (163°F). I closed the shut-off valve installed on the collector feed line. This morning at 6:00 AM, I checked again, and the upper sensor showed 16°C (61°F). I reopened the shut-off valve and went for breakfast.
After 30 minutes, before leaving for work, I checked again and, without any sunlight, the upper sensor suddenly showed 66°C (151°F), even though the pump was still off.
The pump normally only starts when there is a temperature difference of 5°C (9°F) between the lower and upper sensors.

Where do 50°C (90°F) come from in 30 minutes if not from the sun? It can only be coming from the storage tank. I don’t want to heat my collectors during winter, but I’m glad if 30°C (54°F) comes from above in winter so I don’t have to heat the full 75°C (167°F).

Does anyone know this problem?
Can anyone help me figure out how to solve it?

This is my first house, and I’m not a tradesman, but something is definitely wrong here—I have enough technical understanding to know that. I can only imagine this is caused by thermosiphoning, like in an old gravity heating system. When the fluid is warm enough, it rises on its own without the pump running and continuously cools down my storage tank.

Regards,
Alex

How does the solar system heat your buffer tank? Through a corrugated conduit?

A possible solution could be a gravity brake in the solar circuit, if one is not already installed.

First, I had to google what a corrugated pipe is. :-)

So, from the collector on the roof to just before the pump, there is a corrugated pipe (supply and return lines are the same length). From the pump to the heat exchanger, copper piping is used.

Okay, what is the purpose of this gravity brake and how does it work?

I will pass this tip on to my installer.

Is that shown in the picture a gravity brake?

Is it correct that this gravity brake is installed before the pump?

The photo shows the supply line from the manifold, and the pump is positioned above it.

Hello

The picture shows a flow meter, which is usually installed together with the pump on the return line to prevent damage caused by excessively high temperatures.
The pump typically also has a gravity brake installed above it.
Some solar stations have the option to deactivate the pump via the shut-off valve located above it.

Please take a photo of the entire pump station.

Olli

Oh, I see…..
Some solar heating systems with auxiliary heating also have a "high summer function."
This cools the storage tank at night to prevent or reduce stagnation in the solar circuit during the day.

Olli