Rheem Tankless Water Heater No Hot Water [Solved]

Your Rheem tankless water heater has no hot water due to overload, built-up sediment, a broken sensor, ignition failure, problems with the heat exchanger, and so on.

Whatever the issues are, you can simply fix them by avoiding overload, resetting the power button, and inspecting the heating elements periodically.

rheem tankless water heater no hot water

If the effort doesn’t bring any luck, go through our article to find out the root reasons behind why your water heater is not producing hot water and solve the issues by yourself.

Table of Contents

Rheem Tankless Water Heater No Hot Water [Solved]

Here, we will discuss the most common reasons why your Rheem tankless water heater has no hot water and show you their simple solutions. Let’s read between the lines…

Note: You can also read how to fix the Rheem Water heater beeping problem.

1. Build Up Sediment

Building up sediment in the water supply lines is one of the main causes of your tankless water heater not getting hot water. It may happen due to long time usage or if your living area’s water is hard or mineral. This may block the lines partially or fully due to overloaded by building up sediments.

Over time, the hard water leaves particulars of magnesium, calcium, and other minerals, which cause jams in the pipelines. Gradually, it becomes stuck in place and reduces the water pressure through the water supply lines.

As a result, your water pipelines, water filter, or pumping system start getting blocked in the water supply and can’t work properly. This can negatively affect the temperature and the water pressure, which makes your heater unsafe.


Check the minerals built up and debris if you live in an area that supplies hard water. Then, clear out the sediment from the water supply lines. At least once a year, descale the appliances to keep them working at their best. Though the process is too complex, you can solve it by yourself. For this purpose, you need to collect all the tools to descale the heater. Such as a hose, pump, descaler, and bucket.

How To Descale A Tankless Water Heater [Step-by-Step]

In order to descale the sediment from your water heater, you might follow the below effective steps.

  • First, turn off the electric power supply unit, gas, and water-flowing parts of the water heater.
  • Make sure the circuit is off.
  • Shut off valves for the unit.
  • Next, release pressure by opening the hot water press relief valve.
  • Now, connect the hose to the hot water supply. Now, put your flush kit in your bucket. Then, connect the hot water parts to the pump inside the bucket. 
  • After having done the steps, let’s run the pump for about 1 hour. This will circulate the cleaning solution and flush out any sediment from your tankless water heater.
  • Now, turn the pump off to dam out and drain any clearing fluid that remained stuck in the system.
  • Finally, repeat the above system in reverse order. This will reopen your valves, turn the water heater back on, and restore the water, gas, and electricity suppliers to the unit.
  • Then, you the removed sediment.

2. Problems With Water Flow Sensor/Units

The next reason for your Rheem tankless water heater not having hot water indicates a problem with the flow sensor unit.

Plus, you will have the minimum flow rate (in gallons) of hot water when the unit shuts off due to safety measures. Because the unit requires a minimum time for flow rate to produce hot water.

Normally, a tankless water heater can supply hot water at a rate of 2–5 gallons per minute. If you face a rate of hot water, there is an issue with your water flow units. On the other hand, a flow sensor is used to measure the presence of water flow.

When there is a demand for hot water, the sensor identifies the demand, sends the signal to the heating elements, and initiates the heating process.

But if this essential element has been damaged or tripped, you will have to face the hot water issue. Fortunately, it indicates a code-12 which means a flame loss. Then, if it gets blocked or clogged, the water flow will be low and you might get a faulty sensor flow error. Again, the blown sensor won’t be able to ignite or the burner won’t stay lit. 


  • First, check if the water heats up properly. If the water heats up, then increase the flow rate to ensure the flow of sufficient hot water. Because tankless water heaters must have a sense of water flow rate to operate initially.
  • To repair or replace the flow sensor, clear out the water inlet filter.
  • When the flow sensor works occasionally the tankless heater could read no water flow. If happens so, Cut it and connect it again.
  • Turn the gas valves switch off, wait for a few seconds, then switch on the reset system and connect to the natural gas line.
  • You just need to be cleaned up the flow sensor then if it is urgent, replace or reinstall the flow sensor to correct the error.

3. Open Fixtures Simultaneously

Your tankless water heater will fail to supply hot water when the hot water fixtures are used too many a time. It may overload your water heater’s flow system. 

For instance, when multiple people are trying to get either their shower, cleaning dish, or towel on at the same time, your shower starts with no hot water. 

Typically, the tankless heater has a flow rate capacity of how much hot water can be used simultaneously. Naturally, an electric water heater takes 1-2 minutes to produce hot water.

As a result, you will get cold water instead of hot water if the heater doesn’t get a chance to pump out hot water.


  • First of all, make sure how many people are using the water fixtures.
  • To fix the issue, you can try using fewer appliances at once. For example, your heater might have shut off supplying hot water because of overloading it.
  • Then you should reset the unit. If the problem is not solved yet, consider replacing the existing water heater with a higher-capacity unit. Hopefully, the overloaded issue will be solved and you will get enough hot water. 

4. Blockage Air intake & Vent

Air supply or exhaust vent blockage is another major culprit for not receiving hot water from your heater. Plus, the vent pipe may be disconnected or have a hole in it which is another culprit for not getting hot water.

When you installed your heater too close to another appliance, it may have blocked your vent air system. Here, the animal pest or birds may have invaded the system space by building a nest or other barrier. Plus, dirty burners are also responsible for this type of blockage.


  • Check the vents and air intake lines for blockage by birds’ nests or debris. After finding any blockages or obstructions with lines, dust bunnies, or other debris, clear them out inside and outside fully to provide hot water.
  • Make sure the vent air intake and the burners are clean.  
  • Recheck the vent pipe connections. If they are disconnected, reconnect them properly.
  • Now, your heater will supply hot water.

 5. Problematic Heating Elements

A defective heat exchanger or the heating element is a common problem with a tankless water heater. Your water heater won’t provide hot water due to problematic heat exchangers. Basically, the heat exchanger takes a while to heat up. You will run short of hot water before it fully warms up.

So, keep in mind that there may be an initial blast of hot water if someone has already taken a bath before your use. Because there is still some hot water left in the faucet after the last usage.

When you are not getting hot water from your water heater, the power circuit breaker may have tripped or is defective. It signals that both the heating elements have run out.  However, you can simply get the solution to the issue.


  • Normally, the heat exchanger takes a few minutes to heat up. So, just wait for 1-2 minutes, and let run the heat exchanger to warm up the water.
  • If it is urgent, you can install a mini-tank water heater by combining your tankless units. It will supply you with hot water while your tankless unit’s heat exchanger is warming up. This step also prevents the “Cold Water Sandwich” issues.
  • But unfortunately, when the heating elements, such as the power and, the circuit breaker, have tripped, call an expert electrician to diagnose and fix the problems. He will investigate them efficiently and fix them safely.

6. Flame Failure

Flame Failure is a basic issue that prevents your tankless water heater from supplying hot water. The failure of the flame is mostly responsible for the ongoing problem.

This might indicate issues with your gas valves, electric wires, and venting system. And then, your water heater shows an Error code-10 which signals that there is a defective flame with the water heater. Let’s see how to fix it.


To fix the issue, inspect the vent to ensure that it is properly connected and ensure that there is no blockage. Plus, check the heat exchanger to ensure the fans, and air intake is clean to the core and performing orderly.

7. Issues With Ignition

Your tankless water heater fails to produce hot water because of failing ignition. You may face ignition issues when the propane tank becomes empty or the gas valves are not open at all.

Plus, you will have encountered it if the electric components, wiring, or sensors are burned out. Because the burner provides a flame to heat the water.

Unfortunately, the burners won’t ignite due to too much flow rate or being jammed by debris. Therefore, you are facing low-pressure troubles with your tankless water heater.

Luckily, a Rheem tankless water heater will show an error code 11 which also means your heater has troubles with ignition.


  • Check if the propane tank has been emptied and the gas valves are fully open and you have paid the gas bill.
  • Check that the unit has enough gas pressure and volume.
  • Ensure there is no dust and debris on the burners. Remove them completely from the burners.
  • Inspect that the ignition operation is working well.
  • Recheck whether the electric components, wiring, or sensors are burned out.
  • After finding they have been worn out, it is a sign of serious electrical trouble. Unless you are inclined to work with gas appliances, it is wise to call a professional. He will figure out the problems and solve them quickly and safely.

8. Leakage In Pipe Line

Your Rheem tankless water heater can’t hold hot water when there is a leak with the valves and plumbing connections. The leak could be a vital reason whenever it is in with the valves and plumbing connections. That’s why the heater can’t supply enough hot water. 

On the other hand, there may be leaks to the water supply lines, nipples, or drain lines. And this serious problem may happen when the temp and pressure release valves become leaky. However, you simply fix it.


  • After investigating any leaks in the water supply lines, shut off the supply lines immediately. And then to fix the issue, you should call a local plumber to inspect the faults, and if needed, he will help you install a new pipe for sufficient hot water flow.
  • Check to see if the pressure release valves have leaked. If the valves are leaked, install a water expansion to reduce the pressure of the flowing water. It will protect your devices from hazardous explosions.
  • If the tip doesn’t work well, change or replace it with a new one.

How To Reset Rheem Tankless Water Heater

Your Rheem tankless water heater may have stopped supplying hot water due to several common issues. This doesn’t mean that your water heater has been damaged or defective. 

So, whenever you will face the common problem of having no hot water, at first, simply you should try to solve the issue just by resetting your water heater. It will back your water heater to the default factory setting. In order to reset:

  • First, take the electric panel out, and keep the gas valves in the OFF position. Then, figure out the heater circuit, and find the reset red button near the thermostat. It also may be hidden at of side of the metal panel on the unit.
  • After finding it, just press and hold down the “reset” button until it clicks and releases. 
  • Now, switch on to start, and finally, most of the common problems why you are not getting hot water with your water heater will be solved.

Maintenance Tips For Rheem Tankless Water Heater

Maintenance is the key to keeping your water heater running perfectly.  Follow our troubleshooting tips whenever you will face that there is no hot water with the Rheem Tankless water heater.

Besides, it is wise to maintain your water heater at least twice a year. Try to keep your heater neat and clean. Inspect periodically so that everything might work properly.

Then, whenever, the solution to any problems is beyond your knowledge or capacity, don’t hesitate to call a certified technician/ plumber to repair or maintain your water heater. He will inspect the troubles and solve them quickly and safely.


How does a tankless water heater work?

When you turn on the hot water, cold water runs through the pipes into the tankless water heater unit. Next, it is heated by gas burners or heating elements. Then, it heats the water quickly and produces hot water.

Why is my Rheem tankless water heater producing too much hot water?

Your tankless heater is producing too much hot water due to the setting temperature being so high, pressure release valves getting blocked or the thermostat malfunctioned. To fix it, simply set the temperature lower or replace your heater thermostat.

Why does my Rheem tankless water heater keep shutting off?

Your tankless water heater is shutting off because there is not enough water running through the unit. This is also a critical issue of overheating. So, check it regularly for your safety.

Why is my Rheem tankless water heater keeping cold?

Your Rheem water heater is keeping cold due to a broken flow sensor. Because, the sensor measures the water and sends the information to the unit’s control board, if it is broken or damaged, your heater will remain cold.

Which temperature is ideal for setting my Rheem water heater?

The professionals suggest setting your Rheem tankless water heater temperature at 130-140 degrees Fahrenheit. Because changing temp frequently may be dangerous for your water heater.


Already, we have sorted out all the most common reasons behind your Rheem tankless water heater’s no hot water issue and showed you their easy solutions. So, whenever you begin to struggle with your Rheem tankless water heater, not a heating issue, simply follow our troubleshooting guide and fix it by yourself. 

Yet, if you face any other issues with your Rheem tankless water heater’s heating problems, don’t hesitate to reach out to us through the comment. We will come to you ASAP with a possible solution.

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