I went to use a seldom used bathtub/shower in my home and it has no hot water. The cold is fine but when I turn the dial to the hot side the flow of water suddenly stops. The sink beside the tub has hot water and operates correctly. I'm in a fairly new house (about 4 years old) and have used this tub very little. About a year ago I had some friends with septic problems use the shower so I know it worked then. Because it is seldom used I can't pinpoint when problem started. All I know is it was fine months ago and now it doesn't work. Any ideas? Thanks.