-1 then 38 flashes - Rheem Tankless Hot Water Heater Rtg-74pvp-2 7.4 Gpm

The issue of the Paloma tankless water heater displaying error code C7 38 may be caused by several factors, including a problem with the thermistor or temperature sensor, an issue with the gas valve or gas pressure, or a malfunction with the control unit or circuit board. To troubleshoot, try checking the thermistor and temperature sensor, and verifying the proper functioning of the gas valve and gas pressure. If the problem persists, consider seeking professional repair or service.

says on tag its lp

Refrigerate between 38 and 42 degrees.

Refrigerate it at between 38 and 42 degrees

If its leaking at 38%, your lucky it hasn't blown up yet. Turn off the gas and replace the water heater.

1) Copy following link for Rheem tankless troubleshoot, including ecosense.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

2) Probably needs new circuit board.

3) Product manual usually give list of required yearly maintenance.
Perform the maintenance, just like changing oil on car, and then service technician is familiar with your water heater and can count on your money each year around Christmas.

4) For independence, reliability, cost, and convenience, don't buy tankless water heater, or any other expensive/complicated water heater that requires yearly maintenance, and generally cannot be repaired by homeowner.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Copy following link for general troubleshoot and error codes:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error code 36 does not show in any resource, including 2008 service manual, or 2012 product manual.
Check that remote control display is illustrating the correct number.
For example there is error code 35.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Today's water heaters have more insulation and are larger.

Reliance does not have a water heater 20 x 38.
http://www.reliancewaterheaters.com/lit/spec/electric/R606E0312.pdf

I checked several manufacturers.

American Water Heater has 18 x 38-1/2"
Model #E62-30H-045DV
Shipping weight 77 lbs, but I don't know who sells it.
http://www.americanwaterheater.com/products/pdf/NRESS00308.pdf

Whirlpool from Lowes has a 30 gallon
18" x 45"

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Error code 38 doesn't show with typical error codes.
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error codes are considered start place for troubleshooting.
Contact Rheem:
http://www.rheem.com/products/tankless_water_heaters/customer_support/

GE is made by rheem-so it should be around 38-41 gal per hour-should be on nameplate by gas valve