I recently went on a no heat service call on a Weil Mclain hydronic heat system. It is an older system and the thermocouple was bad. Replacing that got the system working, but the homeowner also said it pops a lot. I am not real familiar with these systems so I am looking for a little guidance. The systems pressure looks good. The area I am in has hard water. Also I could only find one bleeder valve on the system and it has three zones, two on main floor and one in the basement. does this sound like an issue of buildup in the system? If so any recommendations on how to treat?