Plumbing, Water Heaters

Why is My Tankless Water Heater Beeping?

Tankless 1 Lg

You’ve probably heard tankless water heaters referred to as no or low maintenance, but that doesn’t mean they’re problem-free. As with any mechanical device, there is a range of possible issues that can arise. The good thing is that tankless water systems can notify you when something isn’t working as intended.

Your tankless water heater will “beep” and display an error code to alert you to a problem with the system. Tankless water heaters will alert you with an audible alarm when service is required, a component fails, or a gas or water leak is present. You can locate the error code description in the service manual or online.

If your tankless water heater seems to run out of hot water, it’s likely due to increased demand and not an error. However, errors are still possible.

What it Means When a Tankless Water Heater Beeps

The error codes used and their meanings will vary from one manufacturer to another. But the types of problems that occur are broadly similar. You can read about some common issues you may encounter with a tankless water heater in this article. So, let’s get started.

1. There’s a Build-Up of Limescale

The water coming into the tankless water heater contains various minerals, like calcium and magnesium. The water absorbs them as it flows through the ground where these minerals may be present.

The extent to which they exist in your water supply depends on where you live. The levels vary from one region to another. To get the most precise information for your area, you’ll need to check with your local water supplier.

The US Geological Survey uses the calcium carbonate content to determine the water hardness. It measures the content in milligrams of calcium carbonate per liter:

Moderately hard61–120
Very hard>181

You’ll experience a limescale build-up in your tankless water heater in the pipework and fitments if you live in one of the hard water areas. 

It can also happen in areas where the water is softer, but it’ll take longer before it becomes a problem. 

The build-up of limescale can affect the efficiency and economy, as well as the functioning of your tankless water heater.

If you experience this problem, you’ll need to flush or descale your system.

2. The System Has Detected a Water Leak 

If your tankless water heater error code indicates a water leak, there are two possible causes.

One is that you do have a water leak. The other is that there’s a problem with the water leak sensor.

Either way, your tankless water heater may go into shut-off mode. It does this to prevent leaking water from damaging the unit or your property.

Sometimes, the leak will be evident because you’ll find water pooled on the floor near the water heater or inside the casing.

The leakage may be from the heat exchanger or the pipework. In that case, time to call a plumber.

If you can’t see any evidence of leakage, you’ll need to check the leak sensor itself. Make sure the wiring hasn’t come loose and isn’t damaged.

Assuming the wiring looks OK, it may just be that the sensor is wet. So, dry the sensor and any moisture in the heater casing, and start the heater again.

If it works, then you’ve solved the immediate problem. But you may want to look into how moisture got on the sensor in the first place.

If, after restarting the system, you get the error code again, try disconnecting the sensor. Then turn the water heater back on. If the system runs fine without the sensor, chances are the sensor has developed a fault, and you need a new one.

3. The Water Flow Rate Is Too Low

The flow rate of the water is vital to the proper functioning of your tankless water heater.

Each manufacturer should specify the minimum flow rate for the models they supply, measured in gallons per minute.

The heater won’t work if the flow rate is less than the minimum specified for your model. So you won’t get any hot water.

That’s because the system needs the minimum flow rate to open the flow switch, and if it’s insufficient, your heater won’t ignite.

You’ve probably experienced this if you’ve ever opened a hot water faucet only slightly. The water won’t heat up. 

The problem of low flow is the unit’s risk of overheating because there’s not enough incoming cold water moving through the heat exchanger. So, it shuts down to avoid causing damage. The shutdown also prevents what water is flowing through it from being overheated and posing a burn risk.

So, try opening the faucet fully, and you should then get hot water.

But, if you’re opening the faucet fully and still not getting hot water, and the water flow doesn’t increase, there are a few possible explanations for this.

It may be that the inlet filter at the incoming water supply has become clogged with grit or sediment. Cleaning that out should improve the flow rate.

You should also check that the faucet aerators aren’t clogged.

Or, it may be that there’s trapped air in the system, in which case, you’ll need to bleed it.

Another cause may be the build-up of limescale, as referred to above. The accumulation of limescale can clog pipes, impacting the flow rate.

4. You’ve Overloaded the System 

Just as your tankless water heater has a minimum flow rate, it also has a flow rate capacity which tells you how much hot water your household can use at the same time.

If you exceed the capacity of your system, you’ll overload it. The heater won’t be able to meet the demand for hot water for all appliances. Some will get hot water, while others won’t. Often, the system is likely to shut down to prevent damage.

You should calculate your expected simultaneous hot water requirement when choosing a tankless water heater. That is, how many water appliances do you expect or want to use at the same time. You’ll need to include washing machines, showers, baths, and sinks.

If you’ve overloaded the system, but it continues to operate, the only way to improve the hot water supply is to reduce the demand. Turn off faucets, for example.

If the system shuts down because of the overloading, it may reset itself once you reduce hot water demand. If not, you’ll need to do a manual reset. Your user manual should explain the procedure.

5. There’s a Blockage in the Air Supply or Exhaust 

Your tankless water heater has an air intake that supplies air for the combustion process. There’ll also be a fan to draw in air from outside and an exhaust vent to allow waste gases to escape.

If the air intake, the circulating fan, or the exhaust vent are damaged or blocked, the system will give you an error message.

That’s because if the heater can’t draw in any or enough air, it won’t be able to heat the water. 

A blockage in the exhaust vent can trap dangerous waste gases in the system, causing it to shut down for safety reasons.

So, you’ll need to replace any damaged venting materials and clear any blockages.

An accumulation of dust, dead insects, lint, and bird nests is typical for fan and vents blockages.


So, next time your tankless water heater starts beeping, you’ll know it’s telling you that something isn’t working as it should. 

So, check the error code on the display panel. Once you have the error code, you’ll identify the nature of the problem the system has encountered. 

This article highlighted some common problems. For a more comprehensive list of issues, check your user manual or consult your manufacturer’s website.

Troubleshooting Guides For Tankless Water Heater Error Codes


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.