Gentlemen, let me all thank you very much, resetting heater protection helped. The engine is now running as it should. Operation light is on as well as beeping sound. Tomorrow I'll try connecting processor to water supply and see if the rest works. I am now to believe the whole problem was linked to heater protection.

@David, at the moment I have very similar setup, lacking thermometer, but it is easy to check during the process with the second valve. Water temp is pretty constant in my place so I do not worry about it.
Also I have large water tank with heating element which I'm about to connect with processor and eventually run in independently with central heating pump to pressurize the flow.

Thank you all once again, very very kind of you indeed.