Hot water gets cold after a couple of minutes. After a couple of minutes of hot water the water gets cold and a C7 error code appears on the remote control box. I have a residential outdoor propane gas tankless water heater, eco sense model ptg 74xp. I cannot find error code C7 in the care manual.

Richland tankless is made by Rheem.
C7-76 is communication fault with remote.
Turn off power at remote and wait 5 minutes, turn power back on at remote, and see if problem clears.
If problem continues, read below:

Before calling service technician, open following links for troubleshoot resources including error codes, Rheem chat, typical maintenance manual:
http://waterheatertimer.org/pdf/Rheem-error-code-C7-76.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Tankless water heater, more than any other type of heater, need to be maintained.
Maintaining tankless will probably not affect C7 76 fault code, but can prevent many other common error codes.
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf

Generally, C7 is communication problem with remote
Error codes are considered start point for troubleshoot.
Causes can be: Bad remote, bad wire to remote, loose wire connection at remote, loose wire connection at unit, bad PC board.
In no particular order:
Check wire connections.
Disconnect remote and let water heater control temperature at default 120 degrees F, and if no further problem develops, then that might eliminate PC board as source of problem.
Replace wire to remote.
Replace remote.
Call service technician to diagnose problem.
Contact Rheem about PC board and other options.

Before calling service technician, open following links for troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Rheem-error-code-C7-76.pdf

Before calling service technician, open following links for Rheem tankless resources including error codes and Rheem chat.
Disconnect wires from remote to see if system stabilizes. Unit will heat to default temperature without remote.

Error codes are considered start-point for troubleshooting.
C8 76 can mean PC board failure.
76 can mean communication failure with remote control
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf
http://waterheatertimer.org/pdf/Rheem-error-code-C7-76.pdf

Before calling service technician, open following link for Rheem troubleshooting resources, and contact information:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error codes are considered start place for troubleshooting:
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf
Error code troubleshoot indicates: replace PC board if water heater does not function without remote.

Add a comment and say what you did to fix problem.

Error code 76 has to do with communication fault with remote
Error codes here: http://www.palomastore.com/paloma_error_codes.html

Use following link for Rheem tankless troubleshoot: http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

I believe error code C7 is same as error code 76

Add a comment for more free help.
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For a price, expert works with you while you work on water heater or any do-it-yourself project.
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called Rheem and after giving them the info they are shipping out a replacement board which I can install, hopefully today..to overcome the hot water problem for the short term I disconnected the remote wires at the heater which lets the heater keep producing hot water albeit without the remote...I will keep the old board as backup in case this happens again as there seems to be problems with the PCB

Contact Paloma/Rheem customer (800-432-8373) support and notify them you are getting a code "76" error. Rheem has recently extended the warranty on the "Burner Control Assm."; which is your problem. The C4-C8 portion of the error code, is where the unit stops the ignition process...burner fails to light, or gives you intermittent hot water. In either case, contact customer support. However, I do have a detailed process on how to repair the printed circuit board yourself. Any further questions, you're welcome to email me at [email protected] .

Good Luck, if this has helped you in any way...please indicate so.

Unplug unit from wall. Disconnect remote wires from circ board, and let unit set for about 5 minutes. plug back in. run water and see if unit comes on.

I had the same problem with my tankless waterheater (flashing c4 76 alternately). I called Rheem
tech support and they had me 1 power down the remotepanel 2 unplug the unit from the wall 3 remove the cover 4 remove the wires for the remote panel from the circuit board and pull the twisted pair that goes to the remote out from the bottom of the unit. 5 reinstall the cover 6 plug the unit back
into the wall and turn on the hot water see if it works. It did in my case and they are sending me a new remote panel. I hope it helps.........