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Old 06-24-2022, 08:08 PM   #1
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Location: Hood River
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M.O.C. #31191
On Demand Water heater not performing

Just bought a 2014 3850FL and it is great. One issue though is the on demand hot water system. It is a Precision Temp Model RV-550.
It heats up the water just fine to start a shower - maybe too hot! But after a few minutes it turns cold. Then back to warm then back to cold. If I leave the flow of water restricted it will stay warm enough to finish the shower but that is about it.
Propane tanks are full. Water pressure at the trailer is about 42 pounds. Any thoughts?
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Old 06-25-2022, 05:24 AM   #2
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This water heater was probably not the OEM water heater that came with that unit. It probably replaced the original. Do you have manuals or receipts from the original owner? The Precisiontemp website has some good manuals available for download, and there is a troubleshooting guide for you to follow. The control circuit board has a red and green LED lights that will blink for certain trouble codes. I briefly glanced thru the manuals and did not see the location of the circuit board, so it must be inside the sheet metal box, possibly accessible thru the access panel on the side. (2nd pic)

I also found several YouTube videos about the unit. You should watch the installation video - very few things to hook up. I am not familiar with your unit but it is likely accessed by removing the bulkhead wall in your basement storage area - that is how I get to my Dometic IW60.

Here is a screen shot of the website and manuals available. There is a 2 year warranty to the original owner, but if you are within that 2 years they might help you with parts anyway.
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Old 06-25-2022, 09:23 PM   #3
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M.O.C. #31191

Way more great information that I expected. i am not at the 5th wheel for a few days but when I get back I will check for the error codes.
I really appreciate the time you took to provide the inforamaiton
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Old 06-26-2022, 05:56 AM   #4
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M.O.C. #30449
You mentioned the water pressure was about 42 psi, is that connected to city water or running on your pump? If the pressure is fluctuating and dropping too low, it will turn the on demand heater off; you would have same effect if you turn water off while soaping up like a navy shower. An on-demand water heater needs to run constantly while showering.

I've never worked on an RV demand water heater, but have worked on a few residential models. A very common problem is the flow meter; they all use one to restrict flow down to the point of their capability. These flow meters are usually a turbine style meter an will get clogged up over time especially if you are in an area with hard water. Fortunately these are usually not very expensive and fairly easy to replace.

Take a look at the owners manual, most all demand water heaters recommend a periodic cleaning; hard water build up is detrimental to the flow meter and heat exchanger. White vinegar or CLR are a good choice.

I just looked at the heat rise for that unit, at a 50 degree rise it is only recommended for a little less than 1 gallon per minute to slightly over 2 GPM. That's enough for a restricted flow shower, but make sure no other hot water is being used while showering.
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