Help with Rheem gas water heater error codes

by Ramon

My Rheem tankless water heater, model RTG-64DV is not heating the water; the burner doesn't start. Every time when I plan to use hot water for shaving, my Rheem tankless is not working, it shows the error code 15. When I am taking a shower no problems at all.

What is going on?

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Dec 05, 2020
6-3 error
by: SteveYosh

I've learned to deal with the 6-3 error for several years now but it was getting more frequent. I replaced the pressure sensor but still had the same problem. Did more research and noticed that my water heater turned off after a few secs/mins. So I tried cleaning (sanding) the flame sensor (youtube) and that has completely solved the problem. If any of you have the same problem, hope this will help.

Sep 02, 2019
6 flashes, then 3 flashes
by: Kent

Follow up from my last post. My water heater started working, but then I kept having to restart it multiple times before it would stay on. So I called Rheem and they sent me a new controller. It didn't help. Then they sent me a new pilot light assembly, which I was sure wouldn't work as the pilot light was working. But I installed it anyway. I think their techs just read off a list of things to try. When I was replacing the pilot light assembly, I noticed the small strip of insulation behind the front cover of the pilot light assembly was about gone. So I bought some pipe insulation for about $6. Cut a strip about 12 inches long and then cut it width wise in half. Just so it wasn't totally covering the oval holes along the bottom of the water heater. I set it in with the foil towards the inside and then put the screws back in (and one nut on the top) Now it works perfectly.

Aug 11, 2019
6 flashes, then 3 flashes
by: Kent

My Rheem water heater would start and stop 3 times. Then flash 6 times and then 3 times. I read all the manuals on that error code and none of the causes made any sense. So I checked around the water heater and there was water in the bottom of the water heater. I had a slow leak. I fixed the leak and dried out the water and it started working.

Jul 26, 2017
Controller Intermittent Failure
by: Ottawa Gas

Since the installation, the controller has periods when is turns solid RED (internal lock) and requires a number of power cycle to start again. It is few years old now and the number of power cycles just increased. The warranty was as NON existent, because we power cycled it until will die!
The controller price officially is more than 50% of the unit price (officially) which doesn't make sense.
Not a happy customer!!!!

Jan 29, 2013
Rheem 27
by: MKH

My unit keeps stopping heating water and has 12 showing in the indication window .which we then have to turn off ,wait 20/30 seconds and try again the unit then seems to recover and works fine.

This type of system works well apart from the draw of time waiting for hot water if you have any way to reduce the waste would like to hear .
The unit is 8 months old.

So before a call out thought to find a answer.
Any ideas for these problem would be most helpful

Mar 18, 2011
Low water flow doesn't start tankless water heater burner
by: Anonymous

I agree with Pat. Either using gas or electric tankless water heater you will have the same problem unless you provide minimum water flow required.

Tankless water heater are designed with flow sensors to protect the heat exchanger from being burnt.

I have seen many cases where people have installed low flow shower heads or aerators... they simply do not allow enough volume of water to pass through the heater and activate the burner or heating element. Solution is to check and remove the flow restrictors from the faucets or turn the other hot water tap ON while shaving and increase the flow.

I would first measure the water flow at the fixture to see is that a really problem. Just put the bucket under the tap, turn the hot water on and measure how much hot water comes out in a minute.

Did you check sediment buildup, which will reduce the water flow also.

Or, you might have a problem when running several faucets at the same time and the pressure drops in the plumbing line that is using hot water. In this case pressure is not high enough to activate the switch in your Rheem tankless water heater.

Solution for low flow might also be to install a circulatory pump. Navien for example is one of the tankless manufacturers that includes a pump.

Jun 23, 2010
rheem error codes
by: Pat

The error code 15 you are talking about is actually not an error. Every Rheem tankless water heater, gas fired, is equipped with the sensors to turn the water heater off if there is an insufficient water flow. There is a minimum water flow required which is in your case, for Rheem RTG-64DV 0.40 gpm.

Open the hot water faucet more to provide enough volume.

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