Rheem tankless gas water heater code 13: meaning and exact next steps

Model-specific

What is true of this model and not of its siblings

Indoor units

This code applies to indoor units only, which take air from and vent to a system that must be unobstructed.

What the rod sees

The flame rod reads the flame's quality. A weak or lifting flame, from low gas pressure or restricted air, reads as poor combustion.

Rheem's pointers

Its pocket manual names the gas supply and venting and DIP switch 2, the altitude setting.

Reading the flame

The flame rod senses more than the presence of a flame; it senses how the flame behaves. A weak, lifting or flickering flame produces a different signal than a steady one, and the control reads that as poor combustion.

Supply and venting

Low gas pressure, perhaps from an undersized gas line serving many appliances, starves the flame. Restricted venting starves it of air or lets exhaust gases return. Both are installation matters.

The altitude switch

Rheem points to DIP switch 2, which sets the altitude. A unit set for sea level and installed high up burns poorly. A technician checks the setting against your elevation.

Gas line sizing

A tankless heater draws a large volume of gas when it fires at full rate. If the gas line was sized for a smaller appliance, the pressure drops under load and the flame suffers. Installers check the line size against the heater's input rating.

Fuel type

Check that the unit was set up for the fuel it burns: natural gas or propane. A unit converted without the right kit and settings burns badly. The rating plate and the manual list the conversion requirements.

What the unit sees

The flame rod gives the board a signal strength. Poor combustion means the signal is weak or unstable while the flame is present, so the board stops the burner. The reasons are almost always upstream of the heater: gas, air or venting, which is why the installer, not the heater, is often the one to look at.

What poor combustion looks like

A tankless heater that burns poorly may show a yellow, lazy flame, make a rumbling noise, leave soot at the vent or produce a smell. The control senses the flame and the combustion air, and stops when the readings are outside the limits. Causes a technician checks include a partly blocked vent or air intake, a dirty burner or heat exchanger, an incorrect gas pressure and an altitude setting that does not match the installation. None of these is safe to adjust without instruments, because poor combustion can make carbon monoxide.