The hot water shuts down for a few minuts then

I just had this exact problem. It kept getting worse until we had no water. Our Rinnai tankless hot water heater started the same way though, with hot water for a few minutes and then would shut off with an error code 10. We just had to shut the hot water off and then back on, wait a minute or so and we had hot water back for a few minutes. Our unit would come on with a loud vibrating noise and remain until it shut off with an error code 10 (air flow fault). The solution was to remove the blower fan and blow out the squirrel cage. Ours had moths in it. We also vacuumed out the fan housing. Be careful to mark any wires you disconnect and take pictures before removal. Our unit is now almost silent when it comes on and supplies endless hot water.

It sounds like your thermostat on the water heater isn't working properly. try turning it up higher and if this doesn't work I would have a service techy look at it.

this is usally a ignition problem...it is usally the flame sensor or ignitor giving problem..if the unit is still under warranty contact rheem...or have a qualified technician check it out..

I had the EXACT same problem (installed my tankless last winter and worked fine, now this summer it fluctuates, have to turn the shower completely off and then on again to get any hot water and then it only lasts for a couple of minutes!) Argh - it is frustrating!

Here's what I found: the demand for hot water is lower during the summer (hot) months because the "cold" water coming in is already quite warm. You don't need as much hot water to make the shower temp comfortable. SO, my tankless was shutting off due to low flow demand. I've removed the flow restrictor from my shower head and it helped alot but didn't completely solve the prob. Next step is what has been recommended to me by several people but is much more expensive - change the pressure valve on your shower to a temperature valve. Or just wait til winter and it should work ok again :)

these units need lots of flow to start and run. Set the temp on the unit lower and the people in the shower will have to use more hot and less cold which will make the unit more stable.

your coil is plugged, needs to be replaced m,about a 750 dollar job

have you checked the error codes on the heater?
you can do this by powering off the controler and pressing the up and down keys for a few seconds. this should take you into the diagnostics mode scroll using the up and down keys till you find the one that has the letter E on it and that will give you the last 8 error codes write them down and get back to me

Often, this is the result of a restriction of exhaust gases. This type of hot water heater must be adequately vented, (per installation specs). I found this out after taking a number of cold showers. :^( Two years later, and still counting, no more problems. :^)

Error code 13 is "oxygen depletion sensor" activated.
The first number is a sequence indicator.
If you need the training manual I have it and can send it to you.
I got Rheem to send it to me a while back and it is a big help when working with these units.
It covers th RTG-42, 53, 66 and 74.

the temp, control valve is getting to hot!!! there for only let so much hot water go thru, did you take the inner parts out when soldering this in, if not you might have damaged it, and if so need to replace the cartdrige