I’m posting this to provide possible reference for those with an older Hydro-Hot that produces hot water that fluctuates between warm and hot.
For a couple of years our Hydro Hot has not produced hot water at a consistent temperature. It ranged from luke warm to very hot. Taking a shower required constant adjustment of the temperature. I suspected the “stir pump” because the first one failed a few years ago. Three good, factory trained techs have looked at it as we went to various rallies. The first two and I agreed that the pump was working and did not need replacement.
The standard trouble shooting for the stir pump is to check the temperature at the inlet hose and the outlet hose. Even with your hand, you should be able to feel that they are close to the same. You can check it with an IR thermometer and one tech did that.
Last week John Carrillo (
http://heatmyrv.com/) went to work on it at the Ale Trail Rally in Bend. Over the phone and before the service call, he listed the probable causes: too much antifreeze in the coolant, a bad control thermostat, a bad low temp cutoff thermostat, a faulty mixing valve and the stir pump.
When he arrived, he went to work. He did the trouble shooting and a full service “backwards”. He started by ignoring the suspect pump. He checked everything on his list from the easiest to test, to the hardest. He measured and then diluted the coolant with water to arrive at the ideal 40/60 water to antifreeze mix. He tested the thermostats and checked the mixing valve. The stir pump APPEARED to be functioning because both the inlet and outlet were hot.
He then explained that, when all else fails, you change out the stir pump. Even if both hoses are hot, it could be operating at a very low rate. I could be pumping enough to heat the outlet hose and make you think it is working, but not enough to stir the coolant in the tank sufficiently. There is no way to measure or test the pump's volume. Parenthetically, the stir pump that came with my HydroHotwas changed once and is no longer used because it was troublesome.
John’s troubleshooting included something I've not seen before. To measure performance, he ran hot water out of the outdoor shower onto the blacktop and measured the temperature with an IR gun. He knew precisely what the temperature range should be and when the burner would fire and stop. (I should have written down the numbers!) Note that this is a procedure that could not be done at a dry camping rally like Quartzite because you would run out of water.
The old pump has an odd magnetic drive. If the magnet weakens over time, the motor runs but the impeller will not keep up. Taking the old pump apart showed no visible damage or wear.
Changing the stir pump fixed it. For last night’s shower, I set the knob and did not have to change it. This morning’s dishes were the same. I also got balanced coolant, a reset mixer valve and the reassurance that the thermostats and control board were working. As a bonus, I got a replacement for the cracked burner tube and aged boiler cap that was beginning to leak.
