Hot Water From Cold

[Massey16]

We got out camping for the first time this year this past weekend. As such, I ran water through the camper to push out the antifreeze I put in last fall. Then, I switched the valves to fill the hot water heater. After it was full and heated, I noticed a leak from the plug that I couldn't fix by tightening. So, I isolated the hot water tank without turning off the external supply, fixed the leaking plug with plumber's tape, and turned the water back on to the hot water tank. Afterwards, I have noticed that when we turn the cold water on at the sink in the kitchen, we get cold initially, then extremely hot water for a short period, followed by cold. Why am I getting hot water out of the cold? Have I damaged something?

[myredracer]

Massey16 wrote:
That makes sense.

I guess that the next time we camp I will see if it's in the lines or in the faucet. If it's in the lines, doesn't seem like much can be done. If it's in the faucet, I can replace that. Any other comments/suggestions?

As suggested somewhere above, it can't hurt to try adding a check valve on the cold inlet near the HWH. A shark-bite type would make it quick and easy. Maybe around $15 or so. I'd just put it in and keep your fingers crossed. Should be fine downstream a little from the shutoff valve where there is room to cut the pipe. The plastic fitting at the hot outlet at the tank would appear to be a check valve.

I wonder if the existing check valve isn't working if that would have any effect on the situation?

Not sure what the black "thingy" is between the swivel fittings and tank. The existing check valve would be at the top of the tank at the hot outlet.

Still curious why someone went to all the trouble to redo the hot and cold piping and fittings like that? If I were going to that extent and using brass PEX fittings, I think I would have used a decent quality brass check valve. But there are plastic PEX fittings under the sink.

This is a Sharkbite PEX to PEX check valve. One or more competitors make a plastic one. There may be one with a threaded male or female thread on one end, which maybe is what is there now. Definitely many available with threaded female on each end (non-Sharkbite).

[Massey16]

That makes sense.

I guess that the next time we camp I will see if it's in the lines or in the faucet. If it's in the lines, doesn't seem like much can be done. If it's in the faucet, I can replace that. Any other comments/suggestions?

[Old-Biscuit]

With a cold water inlet shut-off valve at water heater....doubt you have a cold inlet check valve.

Without a hot outlet shut-off valve.....check valve is part of the connector on water heater at hot outlet.

[Massey16]

It's a little dirty back there!

I've only noticed it on the kitchen faucet, but I haven't specifically tried on the others. The kitchen faucet has individual hot and cold valves.

There is nothing else near here that would heat that cold water line. The hot water heater is located just to the left (from looking under the kitchen sink) of where the cold water comes into the camper.

I'm guessing, as others have suggested, that the check valve running to the hot water cold inlet is bad. Does anyone know if it would be the white or black part shown in the pictures?

[beemerphile1]

Is this only happening with one faucet or all faucets?

If only the kitchen faucet, do the water lines run behind the refrigerator? The cold water in the line could be warmed by the heat at the back of the refrigerator.

[Old-Biscuit]

Looking at your photos again........

Seems you have access to the lines (hot and cold) going to kitchen faucet.

Place your hand on the cold water line prior to where the kitchen faucet cold line connection on main cold water line.

Have someone turn o kitchen faucet cold water..........do you feel hot water flowing thru that cold water main line as it feeds the kitchen faucet?

If so......hot water is momentarily backfeeding from water heater into cold water line until cold water flow overcomes the hot water.

Then you would need to install a check valve in cold water outlet at water heater (so cold water can flow into water heater but not back out of water heater via cold inlet).


If you can not feel hot water in that section of main cold water line just prior to kitchen feed line then the hot/cold is happening inside your kitchen faucet.

IMO.......kitchen faucet

[mhardin]

Do you have a single handle valve at the kitchen sink, or 2 valves - one for hot and one for cold?

If single handle, the cartridge can get stopped up on one side or the other. Sometimes, you can remove and clear the cartridge. If not, you can replace it.

[JJBIRISH]

I believe there is a check valve on the hot out… no need for the third valve…
Changes may have been to add winterization option…

[myredracer]

Someone has been in there before and modified the piping. There is white-ish and clear PEX tubing which is residential. RV PEX is normally blue and red. Copper PEX compression rings have been used. Residential type PEX shutoff valves have been used.

No real problem with the shutoff valves, but there should be a shutoff valve at the hot water swivel fitting like there is for the cold. In normal (non-winterized) mode, the valve between the hot and cold lines should be off and the other two valves open. It should work in the normal mode as is, but there should be the 3rd valve for winterizing to keep antifreeze from getting back into the HWH. I don't think this is the cause of your issue though.

I can't make out what is between the HWH and the swivel fittings. Can't see the bottom one but the top one looks like there is a shark-bite fitting in there. Maybe a check valve was added? Or maybe two of them? ("Swivel" fittings are the ones with tabs on them so you can undo/tighten them by hand.) Just doesn't look right. On our HWH, the swivel fittings connect directly to the tank. If they added a check valve (or two), maybe one has failed or is in backwards?

If they have made hot and cold piping modifications, what has been done throughout your camper?? It kinda looks like the red hot water line comes out of the HWH then goes up to the kitchen faucet. That would mean only the kitchen faucet would get hot water. Is there a tee hidden behind the HWH that can't bee seen? The incoming cold line and connection to the kitchen sinks looks like it should work fine. From below the city water inlet, it looks like there is a cold water line running to everything else inside??

Hard to tell exactly from the photos, but something may not have been plumbed correctly. One question would be why anyone made changes. It wasn't done by an RV dealer. Was the HWH heater replaced perhaps? Does anything in the bathroom look like it was modified also? Maybe whoever did this just got something wrong somewhere....

[JJBIRISH]

I believe what is happening is, as the water heats and expands some is pushed back into the cold water line…

Maybe there is an insufficient air pocket in the HWT (waterlogged)… this would make the problem worse since the water itself can’t compress… very common situation…

[Old-Biscuit]

Replace the kitchen faucet or live with the hot/cold at faucet.....your choice.

Check valve on water heater (hot out):
1) allows hot water to flow out of water heater into hot water plumbing lines and
2) stops water from flowing back into water heater when 'bypass' valve is open.

[Massey16]

So, the check valve may still be working as I am getting hot water out of the cold, not cold out of the hot. Next time I camp I could bypass the water heater tank and see if I get any water in the tank.

Is there any point in replacing the faucet if it just goes to back to cold after a short period? Would there be a broken check valve entering the hot water tank that could be pushing hot water back that way? Seems like a long way for the water to travel.

[Old-Biscuit]

Massey16 wrote:
Is there a way to check the faucet itself?

I'm just assuming there must be a check valve btw the valve and the hot out for winterizing.

I know they're full turn because they take more than a quarter turn to stop traveling up or down.

Your water heater has 2 shut-off valves. 1 on cold inlet and 1 on bypass line..therefore there is a check valve in hot outlet connection on water heater tank.
Check valve is installed in lieu of another shut-off valve.....so when water heater is bypassed water does not flow into water heater via hot outlet.

Typically problem with the check valves is clogging/failing and NO hot water.

AS for checking your faucet.......not really. One can replace seals/cartridge IF faucet is rebuildable. Most RV faucets are not.
Replace it with a residential faucet.........Moen, Delta, Price-pfister etc.

[Massey16]

Is there a way to check the faucet itself?

I'm just assuming there must be a check valve btw the valve and the hot out for winterizing.

I know they're full turn because they take more than a quarter turn to stop traveling up or down.