[leman_opc]

Just to update this: after my tests with setting the pump constantly on for some time the flow improved and the system works flawlessly for almost a month now.

I still fail to understand the background of the issues I had, nevertheless I'm not planning on taking the whole thing apart while it works OK. I'll further update this if I face the flow problems again and post the results of pump disassembly then.

Thanks for all the support / suggestions in the meanwhile!