Jim, your Hydro Hot should make consistent hot water until you run out of diesel. You should be able to shower for a couple of weeks straight!
A couple of years ago, mine stopped making "hot" water and started to produce only "warm". The Beaver Coach Sales Service Center had trouble figuring it out. They decided to replace the mixing valve on the back of the unit because they thought it was "stuck". It didn't get any better. Then they zeroed in on the "stir pump" and replaced that, which fixed it.
The new mix valve came with a tag on it that said it should be "exercised" by twisting the knob and resetting to the same spot once a year. That suggestion does not show up in any of my Hydro Hot books.
The stir pump is located at the lower right front corner. It looks similar to the pair of circulation pumps on the left. Its purpose is to "stir" the coolant in the tank when there is a demand for hot water. As I recall, trouble shooting is simple. With your fingers, test the temperature of the hose attached to it when the system is not making heat or hot water. Turn on the hot water at the sink. The stir pump motor should run and the hoses attached to it should get warmer to the touch. On mine, the motor ran but the hoses didn't heat up. The old pump was dismantled and the unusual internal magnetic clutch assembly was in bits! The motor was running but the pump was not pumping.
My opinion of the Hydro Hot varies. When it is working, it is one of the best systems in the coach. When it malfunctions, it is by far the worst system in the coach. It is very hard to find technicians that truly understand the maze of pumps, sensors, switches, hoses, lights, circuit boards, relays, etc. One exception is Roger Burke who has developed a business and Yahoo group around the Hydro Hot.
Roger maintains a full inventory of parts that he sells at a small discount and he will coach you on doing repairs. My electric element failed. Replacement should have been simple if Beaver had not neglected to install a coolant drain. With Roger's help we invented a way to drain the coolant without a drain! Roger also rebuild components and sell them where appropriate. He writes.pdf files covering routine repairs and service for download. For example, the frequently failing float switch has an easy temporary fix with a "jumper" wire that will get you by until you can do the full repair. The fun part of Roger's approach to the Hydro Hot is that he is the administrator for his Hydronic RV Heating Yahoo group. If you join, you will get frequent emails about real issues being fixed with advice from him and others. Over time you will begin to understand how the darn thing works!
