Mod #78: Shower Hot Water Supply Check Valves

Mod #78: Shower Hot Water Supply Check Valves

Submitted on: 04/12/09

     Category: plumbing
Mod Rating: 12345

(17 ratings)

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Mod Description:

This mod comes to us courtesy of senior member professor95, otherwise known as Randy Agee, and is copyright with all rights reserved.

Showering in a RV generally requires a concerted effort to save water – especially hot water. For that reason, it is appropriate to wet yourself down, turn off the water, lather up and then turn the water back on to rinse. Of course, the best way to turn the water off and on is with a simple valve at or on the shower head. Turning both the hot and cold water faucets off and on again is too much of a problem.

Mod Difficulty:

We have had or installed an on/off valve at the shower head of every RV we have owned. Each exhibited the same problem as a result of using the shower head valve. When you turned the valve on to resume your shower, you would get a blast of either extremely cold water or scald yourself with hot water. We learned to live with the situation and always made sure we pointed the shower head away from us for a few moments when restarting water flow to avoid the temperature change shock. But, when our grandson scalded himself (not seriously) by not remembering the “system” on our former 2005 Prowler Regal, I became concerned.

Our new Forest River 5th wheel proved to be the worst of the lot. You would get a blast of icy cold water that lasted longer than any of the other campers we had owned. I finally decided to analyze the problem and see if I could come up with a fix.

On the new camper the water hook-up came into the left side of the basement wall. The cold water line immediately branched off and went directly to the shower and wash basin above then worked its way across the camper to the water heater. Heated water was returned to the shower by the same parallel pathway but included branches to the kitchen and laundry hook up. It was evident that when the water was turned off at the shower head that the incoming cold water, which was at a higher flow pressure than the outgoing hot water, would backflow thru the shower faucets or mixing valves and back up in the hot water line until pressure equalized. When the valve on the shower head was turned back on cold water would push back thru the hot water line and mixing valve; you would get frosted until all the cold water that had back flowed was flushed out.

My solution was to install a check valve in the hot water line as close to the shower as possible. A check valve would allow water to flow only in one direction – to the shower mixing valve and would not allow cold water to backflow. I figured that I might as well install check valves in both the hot and cold water lines so that I would be sure the system was balanced.

Our RV, like most others built today, uses a 1/2″ plastic pipe called PEX. Blue lines are cold and red lines are hot. PEX is a pretty tough plastic. When the RV is built, all the connections are secured with metal ferrules that are set with a rather expensive crimping tool. Gear clamps do not work too well with PEX; you simply cannot get them tight enough on the tough pipe to make a water tight blow proof joint. Fortunately, there are several styles of easy to use fittings to repair PEX. These fittings are carried by both Lowe’s and Home Depot.

I found two types of check valves at Lowe’s. Home Depot did not have any in stock.

The first valve had 3/4” pipe threads. It was a nice compact size but was somewhat pricey compared to a second choice for half as much. I had room to use the larger valves, so I elected to go with the lower price.

The valve I selected had 3/4″ slip fit connections. Thus, I had to pick an adapter that would glue in and provide a 1/2″ inside pipe thread. The 1/2” inside pipe thread was needed for the PEX slip on adapters. It was a lot of adapting, but since a PEX type check valve was not available in the store I did not have much of a choice. I wasn’t too happy with the price of the adapters to connect to the PEX pipe. I needed four adapters and they were about $5 each.

Back at the camper I glued the adapters into the check valves with PVC cleaner and solvent. To prevent any solvent from getting into the check valve and ruining it I only applied solvent to the outside of the adapter and then pushed the check valve down on top of the adapter. With the adapters in place, I could thread in the second set of adapters that would attach to the PEX pipe in the camper. I did give the treads a few turns of Teflon tape to help seal against leaks.

The assembled check valves measured 8” long. Again, I had plenty of room to work with so the size was not a problem. I cut 6” of PEX out of each pipe leading to the shower. The check valves with the PEX slip on connectors did just that – slipped on. The directions for these adapters also indicated they could be easily removed and reused.

When I turned the water back on, I was pleased to discover I had no leaks! I turned on the water heater and returned 30 minutes later to test the results.

The check valves eliminated the problem with the rush of cold water when turning on the valve at the shower head. The water temperature I had when I closed the valve was there when I turned it back on.

The total cost of all materials was less than $50. I completed the major part of the job in about an hour. Not too bad to eliminate a 20 year old inconvenience.

TipThere is a downside to installing the check valves. You will not be able to drain the water above the valve by opening a low point drain. When winterizing the RV water system you will need to be sure adequate pink fluid is pumped into the lines above the valve.
It may not be possible to install check valves at the shower water feed lines on other makes or models of RVs due to restricted space or access. Our new fifth wheel was a natural since everything was open and accessible.

ModMyRV recommends these parts for this mod:
1″ Sch. 40 PVC Spring Check Valve S x S
Cash Acme Shark Bite SharkBite Check Valve
All-Purpose Pipe Cleaner
PVC Glue - 12 pt.

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12 Comments For This Mod

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  1. chrisser

    Been thinking about this mod quite a bit lately.

    I’m about to reconnect my shower, and am adding a shower box.

    I’m wondering what causes the water to be able to backup through the other line. Water is not compressible. The PEX lines, while they might give a bit, probably don’t allow enough volume change to make much of a difference.

    My suspicion is that there are two likely places - the air bubble on top of the hot water tank, and an accumulator, if installed.

    So I’m wondering if one set of check valves further back in the system (just after the heater on the hot side, after any accumulator and the water heater T on the cold) would address this problem.

    The benefit, besides the lesser cost of putting one set of check valves in if you have multiple fixtures, and not having nearly the space constraints, is that low point drains could be added just after the check valves, so the system could be completely drained.

  2. p59404

    I installed both check valves about 3 feet from the shower faucet and it works great, no more hot or cold water coming out first. Thanks for the idea

  3. idiotsinc has the sharkbite check valves and a 1/2″ valve costs 14.95. Installation should be less than 1/2hr.

  4. David L.

    It’s nice to see that other people like a nice shower once in a while also, even if we are “camping” I fully intend to use this mod when & “IF” I can solve another problem. That’s the GPM problem! Am I the only one, or is there someone else out there that would like more then 1 gpm in the shower???? There seems to be a restriction in the system, but I can’t find it. It looks like I’d be pressed to change the valves if I wanted to.?? If anyone has the answer to this one - Please advise. Dave

  5. scottm1

    I did this mod, but for some reason it did not make any difference. I made sure that I put the check valves in the lines after all other connectors on the lines that went to the tub/shower faucet. I still got a blast of cold water after shutting off the shower handle then turning it back on. BBBRRRRR. I must have missed something during this install. I used the exact same valves from Lowes that is in the photos. Any suggestions from anybody before I take the basement cover off and look for where I went wrong?


  6. Richie

    I have a couple metal shower heads thats low flow anyways but also has a small handle that completly stops the water from flowing… Saves alot on wasted water not only in your rv but in your home… I think I gave 20bucks for two on ebay… prolly take 30 seconds to install…

  7. Steve Vondracek

    I did this mod with the brass sharkbite check valves. I also have a Forest River so had very easy access to install valves near the shower faucets. I can’t notice any difference. Still get a blast of cold water when re-opening the shower head valve.

  8. Gary

    The Check valves are a great mod that I did to our shower a couple years ago. However, I used 1/2 inch shark bite Check Valve fittings for a very fast and extremely simple install. Especially since the access to the Water lines for the Shower in our Eagle Cap 950 Truck Camper was a little on the tight side. Really helps the cold water surge problem.


  9. 76trombonesjazz

    The valves need to be as close as possible to the shower in order to minimize the effect of differential pressure. I put mine on only the hot side since we were getting a cold blast rather than a hot blast. Seems to work great.

  10. Travis

    I attempted this mod on an Arctic Fox 31D. Installed the check valves about 4 inches from the shower faucet and it didn’t make any difference. Sounds like a great solution and I’m glad it works for the majority but it didn’t work for me.

  11. Olsen

    I found that one of the biggest causes of this is a combination of the check valve in the top of the water heater used in single valve bypass kits and the valve at the shower head that doesn’t close tightly. This combination allowed only cold water to flow and full up fill up the houseI simply added

  12. Olsen

    I simply added a good shut off valve in the line at the shower handle add it solved the problem of Chris flow.

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