Rinnai Water Heater Troubleshooting & How to Guide

Rinnai Water Heater Troubleshooting & How to Guide

Rinnai tankless water heaters are known for their reliability and durability. And with an estimated lifespan of 20-years, the reputation is rightfully earned. The heaters are made from high quality materials that improve their performance and pretty much make them maintenance free.

But this does not mean that they will not break down from time to time. Needless to say, fixing any arising issues is easier than you think. Rinnai water heaters have a self-diagnostic tool that continuously monitors if the unit is functioning properly.

The self-diagnostics tool provides error codes that makes it easier to diagnose and address issues. Keep reading to learn how to use your Rinnai water heater efficiently and how to troubleshoot and fix any problem.

How do I reset my Rinnai water heater?

Turn off all hot water faucets/taps. Press On/Off button twice. Turn hot water back on and test. You may have to try this a couple times to reset the system.

  • Factory reset for the control•r™ 1.0 module

Press and hold the Connect button on the module until the LED blinks WHITE, and then release.

  • Factory reset for the control•r™ 2.0 module

Press and hold the Connect button on the module until the LED blinks RED and WHITE, and then release then QUICKLY tap 3 times.

  • Master reset to clear an error code on a Rinnai tankless water heater
  • Press and hold A and B until P appears (approximately 10 seconds)
  • Press and hold A and B until PLC appears ( approximately 10 seconds)
  • The unit will power off.
  • Press the power button until the unit powers back up.

Note: After flushing water heater, the procedure to reset LC codes: Push the two switches (A and B) on PC Board at the same time for five seconds. The water heater will return to normal operation and LC# count returns to 0.

Check this too: Mr Heater Troubleshooting and How to Guide

Why is my Rinnai water heater not working?

Start by troubleshooting to see if any of the reasons listed below is the culprit and remedy the issue as needed.

  • Make sure that gas and water valves are open.
  • Confirm that the electricity is ON.
  • Ensure power supplies is 120 VAC.
  • Check to see if you have gas and if there are any gas leaks
  • Ensure that all air was purged from the gas line and after the installation.
  • Make sure plumbing is installed correctly.
  • Check to see if the ignitor, flaming road, and heat exchanger are working properly.
  • See if the water pressure is okay.
  • Check for lime scale buildup
  • check if the water heater is set to the correct altitude setting.
  • Lastly, check to see if there is an error code

Once you have verified that everything is working as it should, call a professional to fix the heater.

Rinnai water heater error codes, meanings and fixes

The Rinnai water heater uses a self-diagnostic tool to monitor its operation regularly. When a problem is detected, the error code flashes at the temperature display on the following models: MC-91, MCC-91, and MC-502.  While it flashes at the clock display on models MC-100 and BC-100. With most of the error codes, the unit will turn itself OFF.

Below is a list of error codes and possible solutions;

Error Code 02

Problem: Water heater burner does not operate in freeze protection mode.

Solution: Call a licensed technician.

Error Code 03

Problem: Power interruption during bath fill.  There will be no water flow when the power resumes after the power outage, and the error code 03 appears on the controller.

Solution: Turn OFF water flow on the hot water tap. Press ON/OFF two times.

Error Code 05

Problem: Bypass Servo

Solution: Turn the power OFF, turn the power back ON and fire up the unit. If the error code 05 is still there, the bypass valve is broken and has to be replaced.

Error Code 10

Problem: Reduced or no air supply to the water heater or there is an obstruction in extracting the flue gases out.

Solution: Make sure that the recommended Rinnai venting is used, there is no obstruction in the venting system, no reduction in diameter and lengths. Also, make sure that nothing blocks the venting system or fan, requested clearances are met, and that dip switch and condensation collar are correctly set.

Error Code 11

Problem: Rinnai water heaters are equipped with the electronic ignition, so what went wrong if there is no ignition on the gas burner?


  • Check to see if the igniter is working and that all the wiring connections are OK.
  • Check the gas burner for proper installation and remove debris and dirt if you find any.
  • Check the gas solenoid valve for the short circuit.

Error Code 12

Problem: Rinnai error code 12 is usually associated with flame failure. Where is the problem if your gas water heater was working and suddenly loses the flame?


  • Check the loose wiring for the PC board, power supply, and flame rod.
  • Clean the flame rod from scale build-up and burner from debris and dirt.
  • Check for short circuits on the gas solenoid valve, reconnect all wiring connections.
  • Ensure there is no obstruction in the venting system.

Error Code 14

Problem: Thermal fuse reacts due to excessive temperature.


  • Remove obstructions in the venting system or water flow system.
  • Check for foreign materials in the combustion chamber.
  • And inspect the heat exchanger for scale build-up or wear and tear.

Error Code 16

Problem: Thermal fuse reacts due to excessive temperature.


  • Remove obstructions in the venting system or water flow system.
  • Check for foreign materials in the combustion chamber.
  • And inspect the heat exchanger for scale build-up or wear and tear.

Error Code 19

Problem: Electric grounding

Solution: Check all components for electric short.

Error Code 25

Problem: Condensate trap is full


  • Unclog the drain line, condensate trap, and tank.
  • fix or tighten the sensor wiring harness.
  • replace the condensate tank with the sensor.

Error Code 31

Problem: Error on the burner sensor

Solution: Replace the sensor if it is faulty or the resistance value is not as recommended.

Error Code 32

Problem: Faulty temperature sensor on the outgoing water line


  • Check the sensor wiring for loose connection or damage.
  • measure the resistance or clean the scale build-up.
  • If the error code persists, replace the sensor.

Error Code 33

Problem: Faulty heat exchanger sensor

Solution: check for a loose connection and fix it. Then check the incorrect resistance or clean the scale build up on the sensor.

Error Code 34

Problem: Faulty combustion air sensor


  • Replace the faulty sensor.
  • Make sure that the fan is working properly.
  • measure the resistance in the sensor.
  • clean up any scale build-up
  • fix loose connection or damaged wiring.
  • Remove any restrictions in the venting system.

Error Code 41

Problem: Freeze protection sensor in external units doesn’t work


  • Fix any loose, broken or damaged sensor wiring harness(s).
  • remove any obstructions
  • if there is no proper reading on the sensor, replace it.

Error Code 52

Problem: Solenoid valve problems

Solution: Measure the resistance of the valve coil or fix the damaged or loose wiring and connections.

Error Code 57

Problem: Burner overheat bi-metal switch does not work


  • Check the switch wiring harness for correct condition operation.
  • Replace the sensor if it was faulty.

Error Code 58

Problem: Secondary (condensing) heat exchanger sensor


  • Check the wiring harness for loose, broken or damaged connections.
  • Look for the scale build-up inside the heat exchanger and perform flushing.

Error Code 61

Problem: Fan failure


  • Measure the resistance of the fan motor.
  • check the damaged or loose wiring and connections.
  • Make sure that the fan spins freely.

Error Code 65

Problem: Problem with the water flow control valve

Solution: Call a technician as this Rinnai error code is related to the bath fill function.

Error Code 70

Problem: PC board fault


  • Check the wiring and that all dip switches are in place.
  • Replace the electronic board if necessary.

Error Code 71

Problem: Solenoid valve problem

Solution: Replace the electronic board.

Error Code 72

Problem: Flame sensor failure


  • Make sure that the flame sensor is in contact with the fire.
  • Check for the damaged or loose connections and wiring.
  • Use the sandpaper to clean the deposits on the flame rod.
  • Replace the flame rod if the above steps didn’t bring the fix.

Error Code 73

Problem: Burner sensor problem


  • Ensure there is no damage to the sensor wiring or electronic board.
  • Replace the sensor if needed.

Error Code 79

Problem: Burner sensor problem


  • Ensure there is no damage to the sensor wiring or electronic board.
  • Replace the sensor if needed.

Error Code LC or OO

Problem: Scale build-up in the heat exchanger

Solution: Water in NA is usually hard, so the lime and scale build-up is frequent. If the “LC” error code appears on display you have to clean the deposits by flushing the heat exchanger. Otherwise, replace the heat exchanger. “LC” is the only code from all Rinnai error codes that will allow the water heater to keep running.

Note: some of the error codes and problems can only be resolved by a licensed technician. Do not attempt any DIY solutions that risk voiding your water heater warranty.

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

If you water heater has power and it is still not providing how water, this could be as a result of a number of reasons;

  • The heater is too small to serve all your how water needs.
  • You are running to many appliance needing hot water at once.
  • The heat exchange is plugged causing it to malfunction.
  • Gas supply is inconsistent or shut off
  • Air supply is blocked
  • The ignitor or flame rod is damaged.
  • the gas burner is clogged

Note: if your water heater is still not working after you troubleshoot and eliminate all the reasons above, call a professional to inspect and fix your water heater.

If you get no hot water when only one hot water appliance is running and you have a gas tankless unit, make sure that:

Rinnai tankless water heater control panel not working

Start by checking whether the unit is receiving power from the outlet. then ensure that the power circuit has incoming power of 120 VAC. Lastly, check for continuity with a multimeter and replace any blown fuses.

Rinnai tankless water heater beeping

When your water heater beeps, it also displays an error code to alert you to a problem with the system. potential causes of the beep include;

  • Water heater shutoff
  • Flood prevention
  • Water leak
  • Component failure
  • Gas leak
  • Low fuel

The water heaters will alert you with an audible alarm when service is required.

What is the priority button on Rinnai?

The priority button is located on the temperature controller. It has a green LED that glows, to indicate that the thermostat is regulating the water temperature and the unit is ready to supply hot water. It also locks or unlocks the controller.

Press the priority button and the up button simultaneously for at least five seconds. The display will show ‘LOC,’ the temperature setting, and a diagnostic code will activate. Repeat the process to unlock the controller.

How to clean a Rinnai water heater

Mineral buildup can corrode the walls inside the heating chamber of the tankless water heater. In order to take good care of your tankless water heater, you should clean your heater regularly. Here are the steps to follow when cleaning your Rinnai unit;

  • Turn off the power source for the Rinnai tankless water heater.
  • Then turn off the water valves.
  • Remove the caps from the purge port valve to release the pressure build inside the pipes.
  • Connect the hose line to every valve and flush the heater.
  • Close the purge port valves and reassemble the hater and restart it.

 How to descale a Rinnai water heater

If you live in an area with hard water, then regular descaling of your water heater is necessary. Hard water contains minerals which can lead to lime scale build-up. This will cause the heat exchanger to work harder and more often to provide hot water because it is sensitive to scale.

As a result, it shortens the lifespan of the heat exchanger which is costly to replace. It also increases your utility bills. Additionally, lime scale buildup related damages are not covered in most warranties.

As a general rule, you should flush your tankless water heater once per year to maintain efficiency. If the water hardness exceeds 250ppm, you may find it better to flush two to three times per year. You should also use a sediment trap or water softener.

Follow these steps to descale your water heater;

How to Flush a Gas Tankless Water Heater

Prep the heater for flushing

  • Disconnect the electrical power going to the heater.
  • Remove the access panel and use a non-contact voltage tester to make sure there’s no longer power leading to the terminal.
  • Locate and close the gas isolation valve.
  • Locate the hot and cold shut-off valves and close them to prevent any water getting into the unit while you work.
  • Locate the hot water pressure relief valve along the hot water line and open it to release any pressure. Be careful, as the hot water will be hot.
  • There will be both a cold water service port and hot water service port. Connect hoses to both of these ports.
  • Place your submersible pump into a five-gallon bucket.
  • Connect the cold water hose to your pump.
  • Place the free end of the hot water hose into the bucket.
  • Pour four gallons of undiluted virgin food-grade white vinegar into the bucket.
  • Use one gallon of CLR to three gallons of water as a heavy-duty alternative to the vinegar solution.

Flush the heater

  • Open the hot and cold service ports and turn the pump on.
  • Allow the vinegar to circulate through the heater for a minimum of one hour.
  • Turn the pump off and dump the vinegar.
  • Close the cold water service port and remove the attached hose
  • Open the cold water shut-off valve to flush out any remaining vinegar through the second hose into your bucket for about ten minutes.
  • Close the cold water shut-off valve.
  • Allow the water to finish draining and remove the second hose.
  • Close the hot water service port.
  • Remove the cold water inlet filter and (if present) hot water in-line filter.
  • Flush the filters at a sink to remove any trapped sediment.

Note: You should let the pump run longer if the pump runs at less than four gallons per minute. This breaks down the scale and flushes out the sediment.


  • Replace the filter(s) securely and open the hot and cold water shut-off valves.
  • Replace the access panel.
  • Open the gas shut-off valve.
  • Reconnect the electrical supply.

How to Flush an Electric Tankless Water Heater

Prep the heater for flushing

  • Shut off the electrical power at the breaker.
  • Close the cold water shut-off valve.
  • Open your faucets to allow any water to drain from the heater.
  • Close the hot water shut-off valve.
  • Remove the access panel and use a non-contact voltage tester to make sure there’s no longer power leading to the terminal.
  • Remove the screws which secure the wires to the heating elements.
  • Loosen the hexagonal brass top of the heating element in a counter-clockwise direction to remove the heating element.
  • Inspect the heating elements for any signs of damage. A cracked element should be immediately replaced.
  • Store the heating elements in the cooper chambers of the heater so that they can also be cleaned.

Flush the heater

  • Fill the copper chambers with undiluted virgin food-grade white vinegar.
  • Allow the vinegar to sit in the chamber for 90 minutes to two hours. This will break up any scale on the elements.
  • Drain the vinegar.
  • Replace the heating elements and re-secure the wires.
  • Open the cold water shut-off valve and let the tank fill.
  • Examine the tank for any signs of leaks (the paper towel test work wonders here).
  • Open the hot water shut-off valve.
  • Turn on several hot water faucets and let the water run for about five minutes to flush out the vinegar and clear any air pockets from the line.


  • Turn off all hot water taps.
  • Close the cold water shut-off valve.
  • Remove the cold water inlet filter and flush it under a cold tap to remove any debris.
  • Replace the filter securely.
  • Close the access panel and restore power at the breaker.

How long do Rinnai water heaters last?

The life expectancy (or estimated lifespan) of a Rinnai tankless water heater is up to 20 years. This can be reduced significantly or boosted based on water quality, heater usage, and maintenance routine.

How much power does a Rinnai water heater consume?

The Rinnai water heater consumes between 25 and 65 watts depending on the temperature and flow of water. The tankless water heater has four 7,000-watt elements, for a total electrical load of 28,000 watts. The average electric tankless water heater needs at least 120 amps to operate.

How to take good care of a Rinnai water heater

It is important to perform annual maintenance on your water heater to ensure it is able to work properly and to fix any issues before they snowball. The maintenance will also prolong the lifeof the heater.

Follow these step when performing the annual inspection and maintenance;

Check for Error Codes

The error-code history will let you know if something happened to trigger an error code that you may not be aware of. To check the error code history;

  • Push the Hot Water power button.
  • Then push the down-arrow button.

The unit will show you if there have been any error codes. This will look like an “e” and then the code number in the display on the unit. If there are no error codes, then you can move on to the next step.

Open the front panel of the water heater

Be careful when removing the front panel of your water heater to avoid damaging the tabs holding it. Remove side-panel strips on either side of the front panel by pushing the left side strip straight to the left. and then push the right side strip straight to the right.

Then remove the 4 panel screws to detach the panel. Remove the front panel by tilting the bottom forward and lifting it off.

Inspect the Flame Rod

Inspect the burner to make sure that the flame rod is operating properly. The heart has a sight glass that allows you to peer through it to see tubes inside that are diffusing fire. You should see a clean blue flame coming out of the flame rod into the heat-exchanger area.

The whole heat-exchanger area will should glow like a red flame, and this is exactly what you want to see. You should also see a clean blue flame radiating underneath the heat-exchanger.

Remove and clean the air filter screen

The Rinnai tankless water heater requires fresh air intake to burn propane and heat up water. The air passes through an air filter with a screen to prevent bugs and debris from entering your unit.

Check this too: Insinkerator Hot Water Dispenser How-to & Troubleshooting Guide

The air filter is located at the top right corner of your unit. Check it for removable items and then replace it. A dirty screen will tamper with the air-gas mixture causing the heater to not work properly. You should check the air filter at least once a year.

Remove and clean the cold water filter and flush the heater with vinegar‍

This steps helps to remove any debris or lime scale buildup in your heater. To do this;

  • Turn off both the cold and hot water domestic water valves
  • Remove the cold water valve cap
  • Remove the cold water filter and clean it. Then reattach it.
  • Turn intake and outlet valve back on
  • Flush heater with vinegar
  • Replace the front panel

Note: When reinserting the filter, you should feel the o-ring seat. That is how you will know it is sealed and tight enough. Finger-tight is adequate.