I had a problem whereby the water in the tank would only reach a temp of 94 degs both on electric and gas. I read several posts and looked at all the wiring, cleaned contacts, checked voltages, etc. Everything looked good but still not getting hot water. Well after reading more posts I cam across the "outside shower" comment, that it must be turned completely off or it acts as a bypass. Well I never use the outside shower so for two days i didn't bother to check it. This morning after taking a tepid shower I went out and checked it. Lo and behold, both cold and hot were open about one turn each. I closed them and almost immediately had 140 deg hot water.
The moral of this story is, check the easy stuff first
then if that doesn't resolve the problem, tear it apart.
So if you have tepid water the first thing to do is turn off the outside shower