Water heater runs hot then cold

Water heater was doing fine until I installed a new brass back flow preventer. The orginal plug in the hot water outlet was like the inlet connection. Had no back flow preventer. Just a gray open connection. now when I turn on the hot water I get hot water for about 15-20 seconds then cold water, then warm and then cold. The water in the tank is HOT. Rechecked the installation of the new hot water connection and is correct. Checked the bypass valve and its ok as water will fill the heater. and the hot water valve is open.

Check valve installed backwards??

If all was working okay before the back flow valve was installed, I would remove it and see if it reverts back to normal. Like Rick said, probably the back flow valve.

John

Thanks for input. Yep, the next step is to remove the back flow and re-install the OEM. The spring and everything seems ok.

FYI --I removed the new brass back flow prevernter and the spring seemed to be loose. I installed another one I had and walla it worked great. Just shows to go ya that even if the part is new doesn't mean is can't fail.

Tmcran,
Cheers! Congrats on the fix.

tmcran,
From back when I was a working stiff, we had predictive maintenance on our paper converters. Plotting the predictive failure rate of most items makes a curve the resembles a bath tub, meaning that most failures occur when the item is first used, or shortly after. If they make it through the first few uses then you are usually good to go until the part reaches an age that the failure rate starts to go up again. So it is not surprising that a brand new item is bad.

Tom,
You are correct. I' have had new items fail before but it still surprises me.

I've looked through posts to see if my problem was addressed, and this comes close enough not to start a new topic, but it's not quite exactly the same. Please advise if this should have been a new topic.

Just like the OP, my water is HOT for 10-20 seconds, and then goes to unheated. Makes for very fast dishwashing or showers though. We discovered this on our trip this weekend.

Everything was fine on last trip last year. This time is the first time this year, with a winterizing in between. We are just north of Metro Atlanta. No severe winters here. Lowest temp the trailer experienced was 14 degrees. Winter was mostly in the 30-38 range.

These below are all the relevant facts I can think of. Can anyone advise what else to look at?

It's a Northtrail 31RED, 2009 model year. We've used it since June 2008. This is coming off its third winterization. The heater is gas. There seems to be no problem with gas supply. I see the heater running flame when I check. The flame is on periodically. When I check multiple times, flame is randomly on or off. It looks like normal operation there. I triple checked the by-pass valves. I turned the hot valve off and on. I turned the by-pass valve on and off. I turned on the hot water at kitchen sink (right over heater tank) and turned the hot valve off to check that water flow stops. I verified the shower faucet to be off. I verified the outside shower faucet to be off. Unlike the OP, there isn't any sort of backflow valve on the water tank outlet. Outlet (hot label) looks just like the inlet (cold label).

The symptom consistently repeated itself over the weekend. I thought maybe first time was just unheated tank or maybe wife used up hot water on dishes or something. But it kept repeating for each need of hotwater. I observed the symptom by running water until it's HOT (to check that it's working) and then turned it down and added cold water according to my usage, shower, wash hands, etc. Water gets colder until all hot faucet and no cold faucet is still cold water, taking place over less than a minute or two.

Is there anything else to look at? It's a very strange symptom. (Note: I'm not very mechanically savvy, so extra explanation of terms will be much appreciated.)

Douglas, welcome to the forum. There should be a backflow preventer (check valve) on the hot water side of your water heater. As noted in the previous posts they do fail. They are inexpensive, somewhere between $5 and $10. And not dificult to change. I think it would be worth a shot to buy one and install it.
Come back and let us know what you find.

Peace
Dave

Thanks for quick reply. I guess I'm either looking in wrong place or I don't know what a check valve could look like. If it's an obvious device in-line like a pressure reducer used on the campsite water supply, there's not one on the tank itself. Both hot and cold hoses look the same and connect to tank connectors with plastic screw-on rings. Is this something on the inside of the tank?

How does its failure lead to cold water in the hot line at the tap?

The backflow preventer should look something like THIS.

Peace
Dave

Nothing like that is in-line anywhere between the tank outlet and the first faucet. Both hot and cold lines have plastic rings screwed onto a gray plastic male-male adapter that screws into tank inlet/outlet. Are the small gray plastic parts the check valves?

HERE is a link to a post by mrcomer. He replaced the check valve on his Landmark. Yours should be similar.

Peace
Dave