I have a hot water baseboard heating sytem put in about 1966. I bought this house from my father in law. I had a plumber fix a leak in one of my pipes and he had to turn off the water. Before then I could hear the water moving through the pipes when the heat came on. The heater seems to be working fine but the movement of the water is no longer heard. Is this a problem or the correct way the heater should work?