Rheem Tankless Water Heater Error Code 13: Meaning and Fix

Rheem tankless water heater error code 13 typically points to a combustion or venting anomaly that interrupts normal ignition.

Table of Contents

What does error code 13 mean on a Rheem tankless water heater?
What usually causes error code 13 to appear?
How do you perform quick fixes for error code 13 safely?
What next steps should you try if the error persists?
Quick reference table
When should you stop troubleshooting and call a professional?
What information should you have ready before calling support?
How can you keep error code 13 from coming back?

What does error code 13 mean on a Rheem tankless water heater?

Error code 13 indicates a combustion anomaly or exhaust venting restriction that affects proper burner ignition.

This diagnostic alert triggers when the system detects improper airflow or combustion gas feedback. Meanings can occasionally differ across specific model lines or production years, so checking your owner manual is recommended.

Error code 13 signals a combustion or venting issue inside the unit.
It frequently occurs right when the burners attempt to ignite or ramp up.
Exact definitions can vary by specific model generation and year.
Confirming the exact fault description in your owner manual is advised.
The system enters a protective lockout state to prevent unsafe operation.

What usually causes error code 13 to appear?

Common causes include blocked intake or exhaust vents, restricted airflow, or inconsistent gas supply pressure.

Debris in the outdoor termination hood can restrict the necessary oxygen flow for clean combustion. Additionally, minor fluctuations in gas pressure or misconfigured dip switches can trigger this protective code.

Blocked, clogged, or excessively long intake and exhaust venting runs.
Leaves, nests, or debris obstructing the outdoor vent termination cap.
Inconsistent or insufficient gas supply pressure reaching the appliance.
Incorrect internal dip switch settings for total vent pipe length.
A buildup of dust or soot inside the burner assembly components.

How do you perform quick fixes for error code 13 safely?

Power down the appliance, inspect the external vents for obstructions, and perform a simple system reset.

Always unplug the water heater or turn off the dedicated circuit breaker before inspecting any components. Clearing minor blockages can instantly restore normal airflow and clear the error.

Turn off the power switch or breaker supplying electricity to the water heater.
Inspect the outdoor intake and exhaust vent terminals for leaves, dirt, or blockages.
Clear away any foreign debris found blocking the exterior vent openings completely.
Restore power to the water heater by turning on the circuit breaker.
Open a hot water faucet fully to test if the unit ignites without errors.

What next steps should you try if the error persists?

Check internal wire connections, inspect water flow rates, and verify that ventilation dip switches match your installation.

If external vents are clear, the issue may stem from internal configuration or sensor communication. Reviewing internal components requires caution and adherence to electrical safety protocols.

Unplug the water heater power cord from the electrical wall outlet.
Remove the front metal cover panel carefully to access the internal control board.
Inspect all wire harnesses and sensor plugs to ensure they are firmly connected.
Verify that internal dip switches match the measured length of your exhaust venting.
Reattach the front cover securely and plug the unit back into power.

Quick reference table

Match your specific operational symptom to the most likely cause and recommended immediate fix.

Use this structured matrix to identify related performance symptoms and determine the appropriate corrective action for your water heater system.

Symptom	Likely cause / fix
Error 13 during ignition	Blocked outdoor vent / Clear debris
Code appears intermittently	Low gas pressure / Call utility
Error trips on high fire	Vent length mismatch / Check switches
No hot water at all	Power lockout / Reset appliance

When should you stop troubleshooting and call a professional?

Stop immediately and call a licensed technician if you smell gas, observe damaged venting, or face internal gas valve issues.

Gas appliances require specialized certification to service safely. Attempting unauthorized repairs on gas valves, sealed components, or damaged exhaust piping can create severe safety hazards.

Any time you detect a distinct smell of gas near the appliance.
If exhaust venting pipes appear cracked, separated, or improperly sealed.
When troubleshooting steps fail to clear error code 13 from the display.
If internal components like the gas control valve or circuit board show damage.
When local regulations require certified professional servicing for gas equipment.

What information should you have ready before calling support?

Gather your exact water heater model number, serial number, warranty status, and a list of troubleshooting steps already tried.

Having this critical information accessible allows customer support or service technicians to diagnose your specific unit much faster. You can typically find the data plate attached to the side casing.

Locate and write down the complete model and serial number from the rating plate.
Note the exact date of purchase or installation to verify warranty coverage.
Summarize the specific error codes displayed on the digital control panel.
List all troubleshooting actions you have already performed on the system.
Record the type of gas supply powering your tankless water heater unit.

How can you keep error code 13 from coming back?

Perform regular maintenance, keep outdoor vent terminals clear of seasonal debris, and schedule annual professional inspections.

Preventative care ensures optimal airflow and clean combustion year-round. Protecting your intake and exhaust paths minimizes unexpected error lockouts.

Inspect outdoor intake and exhaust vent caps monthly for obstructions.
Keep landscaping, bushes, and snow piles clear of the exterior vent terminations.
Schedule an annual maintenance check with a qualified service technician.
Monitor water flow rates and clean inlet water filter screens periodically.
Keep the area surrounding the water heater clean and free of dust buildup.

Frequently Asked Questions

Can a dirty water inlet filter trigger error code 13 on a Rheem tankless unit?

clogged water inlet filter restricts water flow volume through the heat exchanger. While it typically triggers flow-related error codes rather than combustion codes, keeping the inlet filter clean ensures proper overall system operation and prevents secondary heating faults.

What should I do if error code 13 immediately returns after resetting the water heater?

If resetting the unit fails to clear error code 13, it indicates an ongoing physical obstruction or sensor failure. Turn off the power and gas supply, then contact a licensed professional technician to test the gas pressure, combustion levels, and internal venting components safely.

Does cold winter weather cause error code 13 to appear on outdoor installations?

Severe winter weather can cause condensation freeze-ups or frost buildup around outdoor intake and exhaust terminals. This restriction reduces necessary airflow, triggering combustion safety codes like error 13. Inspect the terminals for ice accumulation and carefully thaw them if safe.

Is it safe to continue using hot water while error code 13 is flashing on the display?

The water heater automatically locks out burner operation when error code 13 is active to prevent unsafe combustion. Consequently, the unit will not supply heated water until the underlying airflow or ignition problem is successfully resolved and the error code is cleared.

How do I reset my Rheem tankless water heater after clearing a vent blockage?

To reset the water heater, turn off the power switch on the unit or flip the dedicated circuit breaker off for approximately ten seconds. Turn the power back on, and the system will clear the fault memory and attempt a normal ignition cycle.

Bottom Line

Start by turning off the power and inspecting your outdoor vent terminals for blockages. Clearing any obstructions safely resolves most error 13 occurrences without needing a service call.

Sources

Rheem Owner’s Manual
Manufacturer Support Page
Plumbing Industry Guidelines