About 18 months ago we had a heat pump installed. We had to flush the valve every couple of months when hot water stopped coming out of the tap.

Last month it happened again and we got a plumber out.He opened it up. Inside was lots of soft calcium in balls that broke up easily to the touch.

What causes this? How can I stop it? Will it affect the life of the hot water system? We had an electric hot water system before and had no problems.