Chuck,
We had very similar problem with our coach. We were convinced it was the mixing valve. We had a tech come out and he removed the mixing valve. He told us that the mixing value often times build up deposits from the hard water and make them not function properly. If he replaced it we would have the same problem down the road. The tech took ours off and we had the same problem scalding at the hot water heater and lukewarm inside. We tracked ours finally down to the outside faucets in the water compartment. If they are slightly on (ours didn't appear to be on) you will have this problem. We turned ours on and off and it fixed the problem. Hope this helps you.
Tom
Discovery 40G
