Check valve on Water Heater inlet side?

[dartmouth01]

Hi, I am installing a bypass kit (rig did not come with one) and I noticed there is no check valve on the inlet side.  This might explain why I occasionally would have hot water come out the cold side?  Any harm if I put one on the inlet side, or choose to leave one out (there may not be enough room)?  Thanks!

[Orvil Hazelton]

There's no problem in brazing in an appropriate inline che ck valve to properly control the H2O flow in your system,  PLEASE be sure that it directs the flow in the correct direction. While accomplishing this, some tubular foam insulation might be of help too. Good luch in always improving your home. As always,  oRV  SKP75065

[Dutch_12078]

There's no harm in installing a properly oriented check valve on the inlet side, but I would not braze one in. Check valves can and do fail, so a threaded valve would be a better choice.

[Kirk W]

While it used to be common for RV builders to have a check valve on the inlet side of the water heater, it is more common today for that valve to be on the outlet side, so you may have one there. When the RV comes with a water heater bypass kit they frequently use a 3 way valve to direct water into the tank or past it to the cold water line, such as this one shown in the picture, from Camco on Amazon.                       

In this kit there is a brass check valve instructions tell you to install into the hot water outlet followed by the PVC tee that connects to the hot water lines and one end of the crossover line (white hose). The brass 3 way valve should go into the cold water inlet with the cold water supply connected to the entry fitting and the other end of the crossover to the 90° fitting. The last time that I used one of those kits it came with good instructions and images. It really doesn't matter which side of the water heater the check valve is in since the water must go into one side and out of the other, as long as the relief valve is closed and the tank drain plug is in place. 

6 hours ago, dartmouth01 said:

This might explain why I occasionally would have hot water come out the cold side? 

If there is no check valve in either side it could very well be the reason for this. You should have a check valve in one side or the other just to be sure that your water heater tank will keep water in it if the cold water line should ever break with the water heater on. There are bypass kits available that use a diverter valve in each end of the line such as this one below which have no check valve. 

                          

There are also RVs that come with a bypass kit of the type in the first picture and they also typically use a valve in the wet-bay area where other valves are located which looks similar to the one in this picture. The use of a check valve in the outlet of the water heater allows use on a single bypass valve.

                      

[Ray,IN]

Kirk, that "hot water heater"  label is kinda silly; why would one want to heat hot water_again. Just sayin.

[Dutch_12078]

9 hours ago, Ray,IN said:

Kirk, that "hot water heater"  label is kinda silly; why would one want to heat hot water_again. Just sayin.

Even bringing that up is kinda silly in my opinion. I consider 120 deg.F water "hot", and that's the temperature where my water heater kicks in to bring it back up to the 140 degree cut off after the initial heat up. So at that point it is indeed a "hot water heater" that makes hot water hotter.  

[dartmouth01]

I ended up having to do the bypass install twice, because of defective parts and that the system and area wasn't designed for a bypass to begin with.  The camco valves leaked upon installation, and the plastic check valve I found at the rv store made a horrible humming noise when activated.  Also, the pipe going into inlet side has very little give to it and was a tight fit once the additional length of the 3 way valve and check valve were installed.  I bought the Valterra bypass kit instead, and those 3 way valves are much beefier feeling and hopefully wont fail.  Additionally, i bought a brass check valve and installed it on the inlet side, between the hose and the 3 way valve.  Finally, i cut the pex going into the inlet side and put a flexible SS braided adapter and bridged the gap between the pex I cut and the check valve.  Now, the pressure doesn't spike on the cold side when the water heater heats the water, and I cant drain the water heater using the cold side low point drain (which protects me from the off chance of a cold side leak, and water draining thru that leak, if city or pump are off)

[Kirk W]

3 hours ago, dartmouth01 said:

I bought the Valterra bypass kit instead, and those 3 way valves are much beefier feeling and hopefully wont fail.  Additionally, i bought a brass check valve and installed it on the inlet side, between the hose and the 3 way valve.

I prefer Valterra products to those from Camco also, but used the picture from Camco because it was more clear. I also agree with using a brass check valve as they typically far outlast the PVC ones. 

On the pressure rise from the water expanding when heated, you will still get some of that on theTha hot water side even so. That rise should be somewhat lessened by keeping the proper air bubble in the top of the water heater. On ours I have a check valve on the outlet side of the water heater but installed an accumulator on the cold water side which not only lessens the operation of the water pump but it also minimizes the pressure rise from the water heater. 

Quote

 i bought a brass check valve and installed it on the inlet side, between the hose and the 3 way valve. 

In reading your post again, am I correct that you now have a check valve on both the inlet and the outlet side of the water heater? You must have one at the outlet to prevent the cold water from backing into the water heater when the bypass valve is turned. 

Edited October 18, 2019 by Kirk W