It is a bit out of scope of this project but it pleased me a lot!

Boiller should warm hot water for bathroom too. Usuallly there is third pump what sent hot water to warm up extra boiller for it. I am starting to develop sw procedure to start/stop the third pumpe.

But if hot water boiller is connected to main boiler and placed between up and down lead (pipe) than it is working fully automatic without any valve or electronic. Great, I did not see somethink like this!

Principle is fany. Hot water from backward pipe what going to main boiler climbing up oposite way and replacing cold water inside hot water boiler spiral pipe. (gravity circulation)

There should be manual valve to regulate power volume. Could hot water boiller is able to assume whole main boiler power! It is why there should be throttle valve to slow down heating. This sytem continously keeps hot water boiler full of hot water.

Incredible !