Rinnai tankless water heater goes cold

Rinnai tankless water heater goes cold. Rinnai Tankless water heaters are reliable and durable, and they mainly do not require maintenance that often.

Whether you have an electric tankless water heater or one that runs on gas, this problem can occur in both.

The Rinnai tank-less water heaters are on-demand water heaters, meaning when you turn on the tap or start an appliance, the tank-less water heater recognizes the need and starts to send hot water.

These heaters use heating coils to heat the water. Although this technology is more efficient for heating the water than the standard tank water heaters, which heat the water continuously heats the water.

If your Rinnai tankless water heater is not heating the water properly or the water goes cold, there may be multiple reasons for it.

Rinnai tankless water heater goes cold (Reasons)rinnai tankless water heater goes cold (reasons)

There can be multiple reasons behind the issue of the water heater not providing hot water.

  • If too many appliances are running, chances are that you are running your water heater to its limit.
  • If your water heater is taking a long time to give hot water, it may be because of the pipe length between the water heater and the fixture. Because of the long water pipes, cold water inside the pipes must be pushed forward before the hot water makes its way to the fixture.
  • The inadequate electricity, water, and gas supply could also cause water running cold.
  • If the water pipes are frozen due to freezing temperature, this might affect the water heater’s performance.
  • If the temperature is set too low on the water heater system, it could result in water running cold.
  • Plumbing cross-over can also cause this issue. Cold water is mixed with the hot water from the water heater, resulting in low water temperature.
  • There may be sediment buildup inside the heat exchange.


You need first to identify the cause of this problem. Depending upon the actual cause, we suggest the following solutions to this problem:

  1. If the reason is too many appliances running at once, then the solution is easy. You can choose which activity you need right now and which activity requires hot water can wait.
  2. If you have a blocked exhaust vent somewhere, the notification system in the Rinnai water heaters will notify you. Open the dirty burners and vents and clean the blockage.
  3. If the reason is a power source, check the electrical and gas panel. Reset the water heater if something is causing the breaker to trip. Turn the gas valve full on.
  4. If the outside temperature is below freezing point, cover your pipes for insulation. This will prevent the freezing of the water pipes.
  5. Make sure the water heater has enough supply of gas and water. The water heater should be getting enough water at the correct pressure.
  6. Clean the burners, and remove any dust or debris that may be causing a blockage. Replace the burner if it has corroded.
  7. If you are in a high-altitude area, make sure the dip switch and manifold pressure are set accordingly to the high altitude.
  8. Ensure that the unit receives power from the outlet and the circuit has incoming 120VAC, 60HZ power. You can also check for continuity with a multimeter of both fuses and also replace any blown fuses.
  9. Change the pipes if there is any leakage. This might be causing the water heater not to give hot water.

Rinnai tankless water heater not getting hot enough

To prevent a tankless hot water system from having a “no hot water” issue, the first thing one should do is keep your hot water usage at a reasonable level.

This means that you shouldn’t have all of your water providers going full blast at the same time, as this can cause the tankless unit to overtax itself and cannot sustain it long enough as supplies run out.

At other times, one might come across problems with tankless systems, such as being unable to get hot water because the pump has been clogged because of rust sediment found in hard water.

Rinnai tankless water heater no hot water pressure

Low water pressure is usually caused by the restrictions of deposits that have built up inside of your hot water tank instead. These deposits are created because your faucets are being fed low-quality water.

When the water comes into contact with any heat source within your plumbing system – including but not limited to showerheads or dishwashers.

It’s important to note that the most common cause of this problem is hard water because its composition tends to create more sediment than other types of tap water throughout the year.

Rinnai tankless water heater reset button

To reset your module back to factory default settings, please press and hold the “Connection” button on your module for approximately 4 seconds.

After doing so, you will see the LED on your Sensortag start blinking White. Release it after holding it down for four seconds. Your module will then reset to its original factory setting.

Rinnai tankless water heater manual

Here is Rinnai tankless water heater manual.


Rinnai tankless water heater goes cold. Though Rinnai tank water heaters are a pretty new technology and do not require high maintenance, the problem of running cold water from the heater can be quickly resolved.

This problem can be avoided by periodic flushing and cleaning of the heating unit and the pipes. The solution to the problem depends on the cause of the problem.

Make sure you have diagnosed the right cause before you start to resolve the issue.  If the problem is still not resolved, make sure you get professional help.

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