I have a Bradford White Model M2CTW75T10CN12 with an Armstrong Astro 30 pump and I am not getting any heat. I went to the system and heard the pump vibrating. The pump appears to be installed on the feed side of the hot water heater. On the "hot" side of the hot water heater is a gauge with both temp. and pressure on it. It reads 0 pressure. I tapped the pump and it quit making noise and then I think I felt movement through the system (holding on to the pipes). But I waited 5 minutes and the pump was hot but there was no heat in the pipes to the system which if it was actually pumping I would have expected some in a few minutes. Any help would be appreciated. I have several specific questions. How do you depressurize the system? Which way is the water moving through the tank? How do I test the pump? Could it be the Sparco mixing valve that is clogged? Thanks for any information.