Ok Dennis. Let me try again.
Again it was a '04 Monterey with the HydroHot. Back then, HydroHot meant it was a junior model for an AquaHot. It was smaller, used less fluid in the tank, had on thermostatic switch, used ethylene glycol (Prestone) for boiler fluid and would heat the cabin or the water, but not both at once.
In short, we've had hot water inconsistency due to malfunctions of the mixing valve, the stir pump, control box and the burner itself.
In the beginning and the end of ownership it worked perfectly. Hot water maintained consistent temperature for as long as you wanted to shower. It was as good or better than a stick house. For a lot of the time in between it worked well too.
However......!
The first strange problem with a variety of confusion was discovering several of the screw connectors on the HydroHot board had never been tightened. That was easy to fix and made a significant improvement in overall functionality.
At about year two the water temperature would not stay steady and we went to Beaver Coach Sales. The tech, without any serious trouble shooting assumed it was the "mixing valve" in the back. The mixing valve is borrowed from stick house systems and was made by Honeywell (I think). Since hot water coming directly from the HydroHot is too hot for humans, it has to be automatically mixed with some cold water. The mix valve does not like hard water deposits and can get stuck. The "mix valve" replacement was an improvement, but did not completely fix the problem. The new mix valve came with a label on it saying the selector on it should be cycled annually and replaced to the prefered position. You may be able to make your hot water more consistent by unsticking the mixing valve.
The same tech then guessed it had to be the "stir pump". That is a small, nearly silent, circulating pump. Apparently the smaller HydroHots needed that to keep the boiler fluid consistent when you start drawing hot water. Without it the boiler fluid near the water coils cools too fast. The stir pump replacement fixed it.
At about year 4 or so, several things, including hot water consistency was not right. Previously a fitting in the back had loosened (due to not being tight in the first place!) and was spraying water so that the HydroHot ran in a steam bath for awhile. Beaver had put the Webasto control box in the bracket upside down! That allowed enough moisture into the sealed box and the tiny mechanical relays were having a hard time and early death. A new $900 box fixed it!
Somewhere around year six, we were having some minor trouble. Apparently the burner was not lighting consistently. The boiler fluid temperature would drop too far for consistent showers. No specific repair was done because a routine service seemed to have fixed it.
At about year 8, showers were good only if you let it run long enough to get the burner to fire. Over two years I had three (certified by AquaHot) techs look at it. All agreed the stir pump was working because the outlet hose was hot. The forth tech at about year 10 agreed to completely troubleshoot.
He did the following.
- He measured the concentration of antifreeze. Each time I added a little I used 50/50. But, it is the water that evaporates so the mix had become more like 70/30. It got better! Better was measured by running hot water at the outside shower and measuring it with a thermometer.
- He measured a variety of voltages and pressures, including fuel pressure. No change.
- He did a complete service of the nozzle, burner and filter including replacing a cracked burner tube. No change.
- He determined that everything was now as good as it could be.....except maybe the stir pump. It could be pumping enough to keep the outlet hose hot, but not enough to do the stirring. He put on a new, improved and heavy duty model. It worked! Showers were perfect again and remained so until Rick LaLande and his wife bought it. He wrote in an email that it broke again!
In between the shower consistency episodes, the electric element failed, plastic connections in the back split, the relay for the electric element failed, the high limit safety thermostat failed, the "old school" extra large boiler cap failed (twice), the (cheap) overflow tubing failed, the low fluid sensor died and a bearing deep inside the burner failed.
I spent a lot of "quality time" with our HydroHot!
Based only on our experience, I would suggest:
1. Make sure the burner fires every time the system calls for it. With our HydroHot both the electric and diesel worked together. I could look at the amps on the Alladin and see if the electric element was being used. If it was, and the diesel switch was on, the burner would be running too.
2. Get to the mixing valve and make sure the knob rotates. Do make sure you put it back where it was when you started. Some say it can be carefully wiggled with big pliers to break it loose if stuck.
3. Based on what for me was a high failure rate, a new stir pump may be what you need. The stir pump is a gamble because it is nearly impossible to test it for full capacity.
Good luck!