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heating and AC, plumbing & electric 479.900.0784
December 4, 2021

Tankless Water Heater Not Working or Heating? Here's What to Check First.

Is Your Tankless Water Heater Causing Issues?

There are arguments for investing in a tankless water heater including the fact that it generates hot water only when you need it—and for as long as you need it—saving 27 to 50 percent of fuel costs over tank-type heaters. (A typical gas-fired tank wastes 40 to 50 percent of the fuel it burns.) Tankless water heaters take up much less space than storage water heaters as they heat the water directly. When you turn on the hot water, the cold water travels through a pipe and into the tankless water heater unit where it is heated by a gas burner or an electric element. This allows you a constant supply of hot water.

In this article, we’re going to discuss a few common issues that homeowners experience with their tankless water heaters. We have produced a short video highlighting some of these issues and ways to fix them below.

Tankless water heaters are energy-efficient, have low maintenance costs, and are reasonably durable. But just like any appliance, they’re not completely  immune to issues. From time to time, they may present with minor problems, such as having no hot water, or not firing. Tankless water heaters, also known as demand-type or instantaneous water heaters, provide hot water only as it is needed. They don’t produce the standby energy losses associated with storage water heaters, which can save you money.

Tankless water heaters heat water directly without the use of a storage tank. When a hot water tap is turned on, cold water travels through a pipe into the unit. Either a gas burner or an electric element heats the water. As a result, tankless water heaters deliver a constant supply of hot water. You don’t need to wait for a storage tank to fill up with enough hot water. However, a tankless water heater’s output limits the flow rate.

If your tankless water heater isn’t performing up to par here’s what you should check. 

No hot water coming from taps, or water is lukewarm

What’s the issue when you have no hot water in house but have cold water? This is the most common problem you can expect with a tankless water heater. To get to the root of the problem, ask yourself the following questions.

How many appliances am I running at once?

If you’re running the dishwasher, doing a load of towels, and showering at the same time, chances are you’re just running your water heater to its limits. Every tankless water heater has a flow rate capacity that should give you a good idea of how much hot water can be used simultaneously. Choose which hot water activity you need right now, turn off the others, and restart your unit. Many times, this is just due to too many faucets being run at once, like your shower and the kitchen sink. For example, taking a shower and running the dishwasher at the same time can stretch a tankless water heater to its limit. To overcome this problem, you can install two or more tankless water heaters, connected in parallel for simultaneous demands of hot water. You can also install separate tankless water heaters for appliances — such as a clothes washer or dishwater — that use a lot of hot water in your home.

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Am I reaching my minimum flow rate?

The minimum flow rate is the amount of water (in gallons) the tankless unit needs flowing through every minute to produce hot water. If you’re asking for less than the minimum flow rate, the unit is probably shutting off as a safety measure. Increase the flow out of your faucet and wait to see if the water heats up. Tankless water heaters must be able to sense water flow in order to initiate operation. Most models will operate with flow rates as low as 0.5 gallons per minute. This is the lowest minimum flow rate in the industry and is an important benefit.

Typically, tankless water heaters provide hot water at a rate of 2–5 gallons (7.6–15.2 liters) per minute. Gas-fired tankless water heaters produce higher flow rates than electric ones. Sometimes, however, even the largest, gas-fired model cannot supply enough hot water for simultaneous, multiple uses in large households. 

Is something plugged up?

Check your vents and air intake channels for blockages. Lucky for you, most tankless water heaters have notification systems that tell you if you have a blocked exhaust vent somewhere. Make sure everything—inside and outside—is free of blockages, dust bunnies, or other debris. Dirty burners are also a source of blockage. Make sure they’re clean!

What about my power source?

If you’re running on electricity, check your main electrical panel. Something may have caused the breaker to trip, requiring a reset before your tankless water heater will work again. If you’re burning gas, make sure you paid your bill, there’s propane in your tank, or the gas valve is fully in the ON position.

Is it cold outside?

In the winter, frozen water pipes can prevent hot water from reaching you and your appliances. Safely and naturally thaw your pipes before trying again for some hot water.

Water temperature in your house is too hot

So what if you’re experiencing the opposite problem? Here are the things to fix if your water is getting too hot:

  • Stop overloading the system by using too many taps at once. 
  • Reset your water heater thermostat to around 120 F. 
  • Reposition your temperature sensor to get a more accurate reading.
  • Clean your tankless water heater’s inlet filter. Follow the manufacturer’s instructions for your model. IMPORTANT: Whichever type of tankless water heater you own, turn off the unit and wait until it cools down before attempting any DIY work on the system.
  • Again, clear any blockages. Reduced water flow can cause any heated water to get too hot. 

A problem specific to electrically powered water heaters is a faulty heater element. Electric water heaters may be equipped with either one or two heating elements. If a heating element begins to ground out, it will stay on all the time and overheat drastically. Not surprisingly, the result will be painfully hot water – and that’s just for starters. With time, the heater element will burn itself out completely. Then you’ll have no hot water at all until the element is replaced.

Mineral or Sediment Buildup in Water Heater

The water heater and the pipes could be susceptible to becoming blocked partially or fully due to a buildup of mineral or sediment. Systems with iron pipes and components can rust and lead to iron sediment building up throughout. Meanwhile, homes with hard water could see minerals like calcium and magnesium resulting in a scale buildup.

Over time, these minerals and sediment can become stuck in place, leading to a gradually growing buildup that narrows the passage that the water moves through. This can affect the pressure and temperature of the water and make it potentially unsafe.

If you are experiencing problems relative to buildup, you’ll need to call a professional to flush your system. This should be a part of your regular annual maintenance so as to avoid more damaging issues caused by mineral or sediment buildup.

Water runs hot, then cold, then hot again. (Hot or Cold Water Sandwich)

It’s the dreaded cold water sandwich, which most often occurs in the shower.  Here’s what’s probably happening: Someone in your home could have showered just before you. The hot water you’re feeling in the beginning is the leftovers from the previous person. Then, the water gets cold again while the tankless water heater is re-heating the water for your shower. Then, once the heater does its job, you get your hot water again.

If this happens a lot or really gets on your nerves, ask your Northwest Arkansas plumber if a mini tank water heater could help. A small tank will give hot water while the tankless unit heats up, preventing this cold water sandwich in the future.

A cold water sandwich effect refers to the phenomenon where the water from a heater is warm for a few minutes, then unloads a burst of cold water, and then the water quickly returns to being warm again. This is a common problem with tankless water heaters. There is some water which remains stored in warm condition at the mouth of the faucet or other outlets, which means when someone runs the tap or the shower, he will receive some hot water instantly. However, a tankless heater takes some time to heat up the exchanger and during that time, some cold water may get through the exchanger and reach the user. The issue at hand is more common to electric water heaters than it is with gas powered heaters. The reason for this is that gas reaches the operating temperature almost immediately, whereas electric heaters may take a minute or two to reach the required temperature for heating.

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Water smells bad or looks discolored (Smells Like Rotten Eggs)

Your water should always be clean and clear. If it’s discolored or smells funky, you might have something like mold, fungus, or bacteria growing inside your unit. The most common bad smell you can pick out is that of “sulfur” or rotten eggs.

This smell is typically caused by sulfate bacteria that can develop within the tank. This issue usually happens when warm water is left too long in the tank and bacteria builds up in the water. The soft water breaks down the magnesium and creates sulfate gas within the water heater

The minerals in our water tend to build up in our units over time. When enough builds up, you get cloudy, yellow, brown, nasty water. If you notice rusty or rust colored water coming from your faucets, then you may have a build up of rust or damaged piped within your unit. Flushing your tankless water heater with a pre-made descaling solution or regular distilled white vinegar should solve your problem. It’s good to be in the habit of cleaning your tankless water heater at least every six months. If you know you have hard water problems, ask us about water softeners to help keep your unit in top condition.

If your rotten egg or bad smell is caused by stagnant water within the tank, then you will probably need to have the water heater replaced. On some DIY websites they may recommend draining and flushing the tank. However, even if you can flush the bacteria out the smell will likely stay within the tank and you’ll continue to experience the same problem

My Gas Tankless Water Heater Won’t Ignite 

Proper gas pressure coming to your tankless heater has to be provided. Check the gas valve and ensure that it is open, and that you have paid your gas bill. Check all sensors, wiring fuses, and electrical components to ensure they have not burned out. Ensure there is no condensation or debris on the burners that may cause them to not ignite. If the flow is too low, the burner will not ignite. Low pressure is one of the most frequent tankless water heater problems and is easy to fix.

Here are the ignition failure codes found on some tankless brands:

Takagi Tankless Water Heater – Error Code 111, 11 or 3

Electric Tankless Water Heater Rinnai – Error Code 11

Navien Tankless Water Heater – Error Code E003

Noritz Tankless Water Heater – Error Code 11

The ignition failure on tankless water heaters can occur to any brand and model, no matter how advanced or not it is. The failure can be caused by a problem inside the water heater or due to an external cause.

  • Make sure that gas and water are open and electricity is ON (120 VAC supply).
  • Confirm that the correct gas type (natural gas or LP) is used.
  • Make sure the pressure is per specs.
  • Verify that all air was purged from the gas line and after the installation.
  • Make sure plumbing is installed correctly, per codes and manufacturer’s instructions.
  • See if the water pressure is per specs.
  • Ensure that water is not too hard (over 7 grains) as it can cause sediment build-up.
  • If your location is at a higher altitude, check out if the water heater is set correctly or as designed.
  • And finally, is there an error code?

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Water is leaking from Tankless Water Heater

Water leaks on your water heater are typically caused by leaking valves and plumbing connections. If you notice a leak, try to trace it to the origin within the plumbing pipes. If it is not immediately noticeable, then it’s advised that you should shut off water to your water heater, and call a local plumber in your area to come inspect the situation.

My Navien Tankless Water Heater Isn’t Working

Here at Paschal, we specialize in installing and maintaining Navien brand tankless water heaters. Navien NPE-2 Series and NPN Series high efficiency tankless water heaters provide endless domestic hot water, all while keeping your utility bills low.

Condensing Tankless Water Heaters

Navien Premium Efficiency condensing tankless water heaters are the #1 selling high efficiency condensing tankless water heaters in North America. The NPE-2 series offers ultra-high efficiency up to 0.96 UEF to keep your utility bills low, endless hot water, and exclusive ComfortFlow® technology with a built-in recirculation pump and buffer tank.

Non-Condensing Tankless Water Heaters

Navien Premium Non-condensing tankless water heaters deliver a continuous flow of hot water for as long as you need it. No waiting for a tank to reheat more water, wasting time and energy. NPN series is the only non-condensing tankless water heater to offer NaviTech™ stainless steel heat exchanger and stainless steel burner for durable and eco-friendly performance.

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Condensing VS Non-Condensing Tankless Water Heaters

  Condensing Non-Condensing
Efficiency Ultra-high Efficiency (UEF up to .96) High Efficiency (UEF > .80)
Venting PVC acceptable 3″ x 5″ metal concentric required
Installation Location Indoor or Outdoor Choice of interior or exterior
Long term operating cost Lower than typical non-condensing tankless and storage tank system Could be higher than condensing but lower than storage tank systems
Durability Stainless steel heat exchanger extend service life Stainless steel heat exchanger extend service life
Dimensions Slightly larger than non-condensing, about 70-80% smaller than tank system Slightly smaller than condensing, 80% smaller than tank system
Initial cost Usually higher than comparable non-condensing Usually lower than comparable condensing
Maintenance requirement Annual service recommended Minimal

How a Tankless Water Heater Works

  1. When a hot water tap is opened, the tankless water heater detects the flow

  2. The flow sensor activates to determine the amount of hot water needed

  3. The igniter activates

  4. The gas control valve opens to supply the correct amount of gas

  5. The fan and venturi activate to provide the correct amount of gas and fuel

  6. The premix burner ignites providing a flame to heat the water

  7. Cold water is pre-heated in the secondary heat exchanger

  8. Pre-heated water passes from the secondary to the primary heat exchanger

  9. The unit determines outgoing set temperature and adjusts the flame to heat the water

  10. Heated water moves to the buffer tank

  11. Desired hot water amount delivered to the faucet

Besides providing hot water where and when it’s needed, the NPE-2 Series offer homeowners the following benefits:

  • Much more energy efficient than old fashioned tank systems
  • Ultra high energy efficiency —
    up to 0.96 UEF
  • Backed by the industry’s strongest warranty – 15 years on heat exchangers
  • Energy Star certified
  • Takes about 80% less space than old fashioned tank heaters
  • Longer lasting than tank heaters
  • Easy to use control panel
  • Elegant, clean appearance
  • Improves resale value
  • Ideal for replacements or new construction

Call Your Local Water Heater Repair Company!

If you’ve tried these DIY fixes or you have a totally separate issue, we’re here to help. Our licensed Northwest Arkansas plumbers can assist you with all your tankless water heater needs. Our plumbers in Northwest Arkansas, Missouri, and Fort Smith work on every brand and make of tankless water heaters, including Navien, Rinnai, Rheem, Bosch, EcoSmart, Stiebel, and more. Call us!

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