Aug 23, 2010 12:57 pm
Re: Need a SHW Installer advice on current issue with system
...usually the head rating of a pump is based on an open system. Basically, if you hooked up the pump to a water source and let it run, the water will shoot up to it's rated height. In a closed loop system you can usually get away with using most any pump since the head pressure from the water column in the piping is enough to compensate for the additional pressure needed. The Taco 007 has a low head rating also which is why a lot of installers use a Grundfos pump. But the Taco is better quality and last a lot longer. I've seen enough cases where pressure in the panels has built up to overcome any pump, which is why purging the air out is important. did you install a float type air vent? This will remove any air that is in the system as the fluid circulates.
Also on hot sunny days, when you use very little hot water, and the water in the tank is hot and the system does not turn on, the fluid in the panels can get very hot and build up pressure. I often tell customers to use up, dump or waste some hot water just to keep the system circulating to prevent stagnation.
As far as the expansion tank goes, if it is a 30 lb tank, the internal pressure should be 30 lb. when empty or disconnected from the system or out of the box, and the system pressure should be less. The job of the tank is to absorb any excess pressure to keep the system pressure steady.