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Rinnai Water Heater Troubleshooting & How-to Guide

Rinnai Water Heater Troubleshooting & How-to Guide

Rinnai has a reputation for producing highly efficient and low maintenance tankless water heaters with a life expectancy of up to 20 years. Their highly-rated water heaters, however, may develop issues when in use. These issues can arise from poor installation and low maintenance, improper use, or component wear and tear. Some fixes are simple to do yourself, while some will require a professional plumber’s help. Read more below on how to troubleshoot your Rinnai water heater.

How to operate a Rinnai water heater

  • Turn the gas valve clockwise to the ‘On’ position.
  • Switch on power to the water heater by pressing the power button.
  • Set your desired water temperature on the thermostat using the ‘Hot water temp’ up and down buttons. Adjust until you get your desired temperature displayed on the digital monitor.
  • To change the temperature scale from Fahrenheit to Celsius and vice versa, press and hold the ‘On/Off’ button for five seconds while the water heater is off.
  • Open any hot water tap, which automatically lights the burner to provide hot water.

Check this too: White Rodgers Thermostat How-to & Troubleshooting Guide

How do I reset my Rinnai water heater?

Resetting the Rinnai water heater will reinstall the unit to the factory default presets and deleted all the current settings.

  • Turn off all the hot water faucets.
  • Press the On/Off button twice.
  • Turn the hot water back on. The water temperature goes back to the factory preset, which varies depending on the model number.
  • You may have to repeat this process a couple of times to reset the system.

Rinnai water heater error codes, meanings, and fixes

Rinnai water heaters have a self-diagnostic system that monitors the unit. When something wrong happens, the heater displays an error code. Keep in mind that error codes vary depending on brand and model. We have compiled an error code guide to help you diagnose issues and remedy tips.

Error codeMeaningRemedy
2The water heater fails during freeze mode protection.Call a professional plumber
3Power interruption during a bath fill; water does not heat after power returns.Perform a factory reset for the water heater.
5Bypass servo fault on water heaters with bypass valves.Switch off the power supply to the water heater.
Turn it back on.Turn on any hot water faucet to fire up the unit.
If error code 5 persists, replace the bypass valve. 
7Circulation flow is below 2.1 GPMCheck the water heater is receiving power.
Check the water supply and ensure the water flow is at least 30 psi.
Check the pump wiring, look for any loose, damaged, or broken connections, and replace if necessary.
Drain the water tank and check the water inlet filter for any blockages. If it is clogged, clean it or replace it.
Flush and descale the heat exchanger. 
10Exhaust or air supply blockageEnsure the venting material is compatible and approved by Rinnai.
If not, replace the parts with Rinnai-approved venting materials.
Check for blockages in the venting system. Check for any loose connections in the venting system.
Ensure the vent length and diameter is within the correct clearance and limits. The most likely reason is a poorly installed vent pipe. 
11The heater does not turn on.Ensure you have the right gas type and the pressure is correct. Make sure there is no air in the gaslight preventing gas from flowing.
Switch off the water heater and drain the gas line.
Check the ignitor is not blocked and generates a spark. Check the wiring connections; the unit is correctly grounded, dip switches seat correctly, the gas solenoid has no short circuit.
Check the burners, ensure they are seated correctly and they are free from debris and dirt. 
12Flame failureCheck the power supply and connection. Ensure the gas type, quality and pressure are correct.
Check for loose connections on the PC board and flame rod wire. Look for a short circuit on the gas solenoid.
Verify there are no blockages in the venting system. Remove debris and blockages from the flame rod. 
13Abnormal combustionConfirm proper installation of the vent system.
Set the dip switch properly according to altitude.
Check the gas supply inlet. Verify the gas pressure is correct. 
14Overheated or faulty thermal fuseLook for airflow obstructions in the vent system and water flow system.
Check the heat exchanger for hard water scaling and flush out the heat exchanger.
Verify the high fire and low fire manifold pressure is correct. 
16Safety shut down due to unit overheating.Look for short cycling caused low flow in the water circulation system.
Verify there are no blockages in the combustion chamber, exhaust pipe, heat exchanger fins.
Flush out the heat exchanger, clean the heat exchanger fins or replace the entire heat exchanger.  
19A faulty electrical grounding.Test all the unit components for a short circuit with a multimeter. Replace any short parts. 
25The condensate pipe is blocked.Inspect the condensate drain line and tank for blockages. Ensure the condensate line has an air gap between the unit and the outlet drain line.
Check for loose or damaged connections between the sensor to the PC board. Replace the condensate tank and sensor. 
30Presence of flammable vaporsSwitch off gas and power to the unit. Check the flammable vapor sensor and wiring harness and look for damages.
If the error code persists after switching on the unit and the hot water tap, replace the flammable vapor sensor. 
31Abnormal burner sensorEnsure the dip switches and high and low fire manifold pressure are correctly set.
Verify the thermocouple milli-volt range are according to the specs. Replace thermocouple. 
32Faulty outgoing water temperature sensorExamine the sensor and check for damage and blockage. Replace the sensor if the problem persists. 
33Faulty heat exchanger outgoing sensorLook for damaged or loose connections in the sensor. Ensure the resistance readings are within specs.
Check for build-up in the sensor and clean it if necessary. If the issue persists, replace the sensor. 
72 A faulty flame sensing deviceEnsure the flame rod is touching the flame when the unit fires. Check the wiring to the flame rod for damage. Clean the flame rod with sandpaper.
Examine inside the burner chamber for debris or gunk that might be blocking the flame at the flame rod. Replace flame rod. 
LC or 00Limescale build-upFlush the heat exchanger.Reset the code temporarily by pressing the ‘On/Off’ button five times. The unit will run for 70 hours straight before shutting down again from the LC error code. 

Why is my Rinnai water heater not working?

Here are the reasons why the water heater is not working and troubleshooting tips:

1. High limit switch has tripped

  • Ensure the unit is receiving power.
  • Reset the unit.
  • If the water heater fires, the switch is the issue and requires replacing.

2. Gas supply

  • Check for gas supply issues that could prevent the unit from inviting. Look for obstructions, check the quality of gas, and ensure the pressure is correct.
  • If the gas is newly installed, bleed the gas line to ensure there is no air.
  • Ensure the gas connection from the gas control to the heater is secure.
  • Inspect for the presence of moisture in the gas line and replace the gas valve if necessary.

3. Moisture

  • Check for moisture in the heat exchanger and on the burner, which causes corrosion and prevents the unit from lighting.
  • Ensure the wiring and connections are dry and replace if damaged from moisture.
  • Flame rod
  • Verify the flame rods are well install and that each is touching the fire when the unit ignites.
  • Replace any corroded flame rod.

4. Vent system

  • Inspect the vent system for any blockage. Remove any debris or sediments that could be blocking the air intake.
  • Check for loose connections and bent vents.
  • Check the type of vent material, length, and clearances.

Why am I not getting hot water from my Rinnai tankless water heater?

Several reasons can prevent your tankless water heater from making hot water. An ignition failure is the most common reason when your water heater does not produce hot water. Some of the problems can be easily fixed by the user, while others may require a professional technician. Here is how to troubleshoot the issue;

  • Ensure the water heater connects to power. Ensure the power outlet is working and there is no short circuit or a blown electrical fuse.
  • Check the gas supply. Ensure there is proper gas flow and the intake connection is secure.
  • If the unit it recently installed, ensure the gas line bleed it adequately to remove all the air blocking the passage.
  • If the gas supply is okay, verify the gas valve going into the water heater is on.
  • Check the water supply, ensure the unit is receiving enough water and at the correct pressure.
  • If you are running too many hot water faucets simultaneously, the unit will not supply hot water to another tap. Run one appliance at a time.
  • Ensure the vent system on the roof has no blockages. The unit requires proper circulation of oxygen and carbon monoxide to heat the water properly.
  • Inspect the flame rods for obstruction. Ensure they are correctly installed. Remove any debris or replace a damaged flame rod.
  • Clean the burners, remove any condensate build-up, dust and debris. Replace any corroded burners, if any.
  • If you are in a high-altitude area, make sure the dip switch and manifold pressure are set accordingly for high altitude.
  • During cold weather or winter, check for frozen elements and pipes. Insulate all the exposed cables and pipes with an insulation jacket.

Rinnai tankless water heater control panel not working

Here is how to troubleshoot a tankless water heater that has a faulty control panel:

  • Confirm that the unit is receiving power from the outlet. Ensure the circuit has incoming 120 VAC, 60 Hz power, and is properly grounded.
  • Check for continuity with a multimeter of both fuses. Replace any blown fuses.

Rinnai tankless water heater beeping

A beeping sound from your water heater is a warning that something is wrong with the unit. Usually, the heater will beep, then shut off to prevent further damage to your unit. It then displays error codes on the control panel. The following are some common reasons and troubleshooting tips for your beep Rinnai water heater:

1. Water leakages

  • Inspect the water heater for any leakages. The leak could be from the heat exchanger or water pipes which a plumber can quickly fix.
  • If there is no evidence of leakage, check for a weak leak sensor. Look for loose or damaged wiring and replace the wiring or the sensor.
  • If the sensor is undamaged, it might be wet. Switch off the water heater, dry the leak sensor with a dry cotton cloth, and the heater casing inside.

2. Limescale build-up

  • Check for limescale build-up from hard water passing through the water heater. Flush the heat exchanger.
  • Check the inlet filter for clogging. Clean the filter to remove debris and improve flow rate and also prevent unit overheating.

3. Minimum flow rate

  • Verify the flow rate of your unit. Tankless heaters have a minimum flow rate and pressure to work correctly. Your water heater should have a flow rate of above 5 GPM and a minimum pressure of 30 PSI. Running the water heater with a very low flow rate overworks the unit and may cause overheating.

4. Overloaded system

  • Just like having a minimum flow rate limit, water heaters also have a maximum limit. Overloading your unit is exceeding the maximum capacity your household can use at a time. To prevent the heater from shutting down, close some open taps to reduce pressure and demand.
  • If the unit shuts down from overheating, turn the thermostat to the lowest setting or turn off power to the heater for about 30 minutes.

5. Low gas level

  • Gas-powered tankless heaters will beep with the fuel level is running low. Refill your gas tank.

Check this too: Rheem Water Heater Troubleshooting & How to Guide

What is the priority button on Rinnai?

The priority button is on the temperature controller. It has a green LED that glows, indicating that the thermostat is regulating the water temperature and the unit is ready to supply hot water. When you turn on the hot water tap, the water comes out at a set temperature.

The priority button can also lock or unlock the controller. Press the priority button and the up button simultaneously for five seconds. The display will show ‘LOC,’ the temperature setting, and a diagnostic code activates. Repeat the process to unlock the controller.

How to flush the Rinnai water heater

Over time, your water heater will accumulate limescale deposits inside the heating chamber and pipes. This build-up will prevent your unit from working efficiently. Your water heater requires a flushing or descaling every once a year and more often if you receive hard water with high mineral components. Here is how you flush your water heater:

Things you’ll need

  • Screwdriver
  • Non-contact electrical tester
  • Five-gallon bucket
  • Pond pump or small sump pump
  • Three, 6-foot long hose lines
  • Adjustable wrench
  • 5 gallons of white vinegar


  • Switch off your unit at the power source.
  • Shut off the main gas supply.
  • Turn off all the three water supply valves to the heater, including the hot and cold water valves.
  • Locate the cold and hot water valves. Gently take out the purge port valve caps from the purge valves.
  • Connect three hose lines to the three water valves and tighten with an adjustable wrench. The hose lines must be long enough to reach the water heater and bucket or pond pump.
  • Open the purge port valves.
  • Put the pump and the open end of the second hose into a 5-gallon bucket.
  • Fill the bucket with 4-5 gallons of undiluted white vinegar.
  • Open the hold and cold water valves and turn on the pump in the bucket to run the white vinegar through the heater.
  • Let the pump to run for 45 minutes and then turn it off.
  • Allow the white vinegar to drain from the unit through the hoses back into the bucket.
  • Pour the vinegar and place the open-ended hose back into the bucket.
  • Open the cold water valve and let the water flow into the bucket for about five to seven minutes.
  • Close the cold water valve and detach the hoses from the inlet valves.
  • Remove the inlet filter screen and rinse it to remove any debris. Reinstall the screen.
  • Return the purge port valve caps onto the purge valves.
  • Open some hot water taps to bleed out any air from the hot water lines. You will hear a spluttering sound, then steady flowing water and, then close the tap.
  • Turn on the gas supply, water supply, and power outlet—test for hot water from the taps.


From this article, you will learn how to diagnose and fix problems that arise when using the Rinnai tankless water heater. Periodic maintenance such as flushing and cleaning the unit will reduce the occurrence of issues or even breakdowns. Make sure you also get a professional technician to help with installation.