Just bought a triangle tube 150s mod/con boiler. I have done all of my calculations and was just about to get ready to start plumbing the system when I looked at the installation diagram and it has a circulating pump on the return side as well as my independent circulating pumps on the supply side!
It is very necessary to maintain the correct water flow through the boiler, unless you want replace it in a year or two. If you run a single loop, then you need some way to maintain the correct flow no matter how many zones are calling. You can also lose a lot of efficiency if the flow is incorrect. By using a primary and secondary pumping and a decoupler loop, as they show in their diagram, you can easily maintain the optimal water flow in the boiler under all load conditions. This is about the best option you have for maximum efficiency.. You need to contact the Tech Support people and make sure you are installing it correctly, or you will void the warranty, and they will be able to tell exactly why the boiler failed. Installing a boiler correctly requires a lot of skill and knowledge if you want them to work properly.
