Tankless Water Heater Not Working? Here’s What to Check

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. 

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

Scenario 1: There’s no hot 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. Choose which hot water activity you need right now, turn off the others, and restart your unit. 

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.

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.

Scenario 2: My water 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.
  • Again, clear any blockages. Reduced water flow can cause any heated water to get too hot. 

Scenario 3: Water runs hot, then cold, then hot again.

It’s the dreaded cold water sandwich, which most often occurs in the shower. (What a great start to your day, eh?)  Here’s what’s probably happening: Someone 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 Toms River 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.

Scenario 4: My water is… different.

Your water should always be clean and clear. If it’s discolored or smells funky, you might have something growing in your unit. That sounds gross, but it’s really common and generally harmless with the right maintenance. 

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. 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.

Scenario 5: I think it’s time to call in the pros!

If you’ve tried these DIY fixes or you have a totally separate issue, we’re here to help. Our licensed Toms River plumbers can assist you with all your tankless water heater needs. Call us!

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Offer valid up to $150. Must present coupon at time of service. Subject to change at any time. Not to be used in combination with other offers.

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Offer valid up to $100. Must present coupon at time of service. Subject to change at any time. Not to be used in combination with other offers.

First time customers!

10% OFF

Offer valid up to $100. Must present coupon at time of service. Subject to change at any time. Not to be used in combination with other offers.

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