Those glowing pictures of continuous hot water flowing from your Hydro-Hot unit aren't quite accurate as time begins to wear out parts and degrade performance.
Hydro-Hot unit installed in a 2006 Country Coach Allure 430
Our Hydro-Hot unit has been thwart with a continuous stream of breakdowns and repairs to include the continuous hot water running lukewarm after a few minutes of usage. Level sensors, control box, turbine motor, limit switches, fluid loss and mystery leaks are some of the issues we have been (and still are) dealing with. In my view these failures shouldn't be occurring in a product so expensive.
The good news is the most recent problem of limited hot water isn't the Hydro-Hot unit at all but the anti-scald valve made by Honeywell.
Honeywell's anti-scald valve with some extra plumbing attached.
The valve shown above was removed from the Hydro-Hot unit on 4/21/2012 and had been bad for about 2 years. This valve automatically mixes cold water with scalding hot water coming from the Hydro-Hot. A control knob on the valve allows adjusting the mix temperature to something well below the 190F that would come from the raw hot water outlet off a fully recovered heat transfer fluid tank. It's intended to be a safety device designed to prevent scalding during a shower. It also helps reduce hot water line fatigue by not pushing the PEX tubing too near its upper temperature limit. In short, you need to have this special valve functioning properly in your system.
Over time calcium deposits and gunk clog the valve which prevents it from working properly. Valves last about 5 years give or take a little depending on how they are used. When the valve fails you'll see reduced hot water flow internally to the valve and the mix temperature will go down significantly. Remember it's a safety device so failure must avoid any possibility for scalding. Two other symptoms of a faulty valve are a stuck adjustment knob and hot water seeming to run out early. As hot water is being used you'll also notice your Hydro_Hot burner not coming on as early as it once did.
Make Sure It's The Valve
The best way to check for a faulty valve is to run hot water while periodically touching the Hydro-Hot's hot water outlet plumbing. Be careful when doing this as the hot water there can be as hot as 190F. If the hot water at the faucet goes cold (or lukewarm) and the hot water feed into the valve remains too hot to touch you have a bad valve. What this test indicates is the hot water supply is good but something in the valve internals is limiting the hot water flow into the mix outlet. Keep in mind the valve has cold and hot water inlets and a mix outlet. Mixing goes on inside the valve using a temperature controlled orifice. In a properly functioning valve, the control knob can be rotated which limits (or regulates) the mix temperature close to a set point (120F nominal). Properly set hot water should feel very hot and burning to the touch but not scalding.
Removing The Old Valve
Once you determine the valve is bad you'll need to replace it. In my case the valve has 3 1/2" female pipe threads. Lots of configurations exist so carefully check your valve and provide a clear description to your parts source. I paid about $100 for a new valve. No these valves ain't cheap.
On my unit the valve was plumbed into the Hydro-Hot's cold water inlet with a 1/2" brass Tee. That means the cold water heat exchanger tube becomes the support for the valve and its associated plumbing. Not really a great idea IMHO because if you break off (or damage) the heat exchanger inlet tube you'll need to replace the entire Hydro-Hot unit. It's a mistake that will cost you thousands of dollars in parts and countless hours of labor. I feared this so much I put off the repair for over a year.
This is a very delicate repair and one slip, wrong twist or too much torque and snap goes the tubing. If you have any reservations about doing it, hire someone with the experience to get it done properly. And good luck to you finding that person! In my case getting the valve off the Tee wasn't an option. Things were just too tight for my comfort level and I didn't want to risk the aforementioned damage. I was, however, able to carefully strip some of the plumbing off the valve to make the assembly smaller. From there I was able to unscrew the Tee from the Hydro-Hot's cold water inlet using a back-up wrench. There was enough room to allow the valve (now stripped of excess plumbing) to spin with the brass Tee. One careful turn at a time I removed the valve. Once I got the valve out I then removed the rest of the fittings.
Installing The New Valve
When installing the new valve you run the same risks as before with snapping off the cold water inlet tubing. To avoid this dilemma, I decided to make a few simple changes to the OEM plumbing. These changes would also make it easier to replace the valve again should that be necessary.
Modified plumbing arrangement to avoid expensive damage.
Using two 3/8" x 1/2" SS braided flex hoses I connected to the inlet and outlet of the Hydro-Hot. This avoided any possible damaging stresses on the internal connections. I installed all the appropriate fittings on the anti-scald valve. With the valve completely plumbed and fittings oriented for convenient hose runs I simply installed the valve. Open all your faucets to avoid water hammer damage while the air comes out. Purge the hot/cold lines at all faucets and don't forget the toilet. Close all faucets and let the system come up to full pressure (45 PSI nominal). Check for leaks, adjust and tighten as necessary.
You could secure this valve with a home made bracket but I didn't bother with that. There really isn't any need for the valve to be rigid. Do make sure nothing is rubbing or abrading, however. To adjust the knob you'll need to loosen its screw and pull the knob up above the large brass hex nut that locks it. Play with the adjustment until you get the hot water at the faucet you like. Honeywell suggests you turn the knob periodically to avoid a seizure.
This fixed our hot water problem for the most part. Long runs of really hot water will still slightly exceed capacity and the water cools a bit. During which time the burner comes on and the hot water recovers quickly. I may have a few other issues with the Hydro-Hot but the anti-scald valve isn't one of them.
For me this repair was stressful and unnerving. I was careful and didn't break anything. Perhaps luck, perhaps skill and I can't claim either for sure. As stressful as this was it wasn't nearly as stressful as hanging around in some customer waiting area while a so called "expert" mechanic goes at it against a ticking clock. I'm glad it's done and a few of the remaining maintenance items I need to address shouldn't be nearly as difficult. Perhaps this will help someone else out there dealing with a cold shower.
Complete slide show HERE