I have two problems. My system is a hot water boiler,3 years old[Buderus,Logano C124} with 3 zones contoled by ESP zone valves. Two of the zones are bsaeboard heat and one is cast iron radiators. Problem #1. When the zone valves close I get a very loud WHOOSHING noise. It seems to happen on any of the 3 valves but is more pronounced on the zone with the radiators.It was suggested by a contractor that I install a delay switch which would shut of the pump 10seconds before the valve closes ,therefore eliminating the water pushing against the valve as it closes. I can't see how this would help if more than one zone is calling for heat at the same time.
Problem # 2. More worrisome. During the night after the system has not run for some time,so the water in the radiators is cool, When the boiler turns on ,pump comes on also ,I get mild banging. The sound is like someone stricking the pipes with a small hammer. Any ideas?