You own a Solesta solar boiler?

Solesta B.V. was declared bankrupt on february 11th, 2020. This was the mail I received:
Beste Lezer,

Bedankt voor uw bericht.
Op 11 februari is het faillisement van Solesta/eindelijk zon uitgesproken. Advocatenkantoor Poelmann van den Broek is benoemd tot curator, voor vragen kunt u contact met hen opnemen.

Met vriendelijke groet.
Since I had installed this boiler the pump has failed multiple times. There has not been one year without several months of downtime due to the slow service of Solesta. Each time the pump stopped turning, taking a lot of current. Now it still turned, but no water was pumped effectively. As all warranty is gone now, I decided to open the tank myself. It seemed that the output hose was pinched off when it became softer by the warm water. Lucky move.

In the standard setup the flow upwards is heavily limited by a throttle valve. Just before that regulator a return pipe is installed for run down of the upward pipe when the pump is of. During pump operation this return pipe is closed with a solenoid operated valve. This consumes about 15 watt. The pump itself takes about 18 watt.

Solesta claimed that a very low flow was needed for the best efficiency. I really doubt this. It puts a lot of extra load on the pump and keeps both collector and downward pipe at a high temperature. It just needs to be warmer than the boiler. Also, air in the pump is not freed easily by the high pressure / low flow setup.

Therefore I have opened the throttle valve remarkedly, and disconnected the power to the solenoid valve. In this situation the pump dumps most of the water directly into the return pipe. Therefore I limited this flow by making an obstruction in the pipe with a small hole and acts as a "leaky return valve". Now the throttle can by used as needed for a flow the user wants. Still the upward pipe is emptied through the return pipe without any troubles.
Having intermittent use of the pump probably saves also the life expectancy. To improve the cooling I have cut away some insulation and pulled out the pump a little bit. Then I placed my own insulation layer in front of the tank. Also I have added a generous layer of insulation over the tank.

In my current setup the upward flow is probably a little bit too high. But to my opinion this might be the best solution for both the pump and the efficiency. It removes all the heat from the collector quickly, and stops when cooled down. Then the pipes drain and heat loss is limited further.
The pump is powered for much less time, and last but not least, the electric valve is switched off now, avoiding another 15 W of needless electric power. The system has become more safe also, by not relying on an active valve.
I have installed two temperature sensors with a z-wave connection myself: one at the collector downward 'hot' pipe and another one at the hot water outlet connection, representing approximately the boiler temperature. The power is observed by an z-wave power plug.