Your pump need to have constant water to live long. Since you mention water are weak also from the incoming (direct), if you operate the pump you maybe sucking air too. And BTW, putting pump direct from main is illegal.

Have you check with syabas why your incoming water pressure are low? Also if you have a incoming filter (sand, membrane, etc) it could also be that issue.

Best to have a small storage tank after the incoming, and your pump after that.

How long was your first Grundfos pump lifespan?

Since you are using it to pump direct to another tank, i don't think you need adjustable water pressure. Just get one that are fully metal build.

This post has been edited by weikee: Jun 9 2015, 06:39 PM