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 Columbia 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. Most tankless water heaters require some form of water softening or other treatment to validate the warranty.

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 Columbia plumbers can assist you with all your tankless water heater needs. Call us!

We found a leak underneath our kitchen sink and was not able to turn the water off. A MasterTech technician was there within an hour. He was courteous and professional and gave us a couple of repair options. Everything he needed, he had with him and the new valves were installed quickly and he was gone. Great repair experience!
Lorry Myers
Lorry Myers
21:01 27 Jul 20
Technician was timely, professional and courteous. He made sure I understood what was going on. And how best to move forward
Zane Whorton
Zane Whorton
19:15 16 Jul 20
Tyson was incredibly kind and helpful. He came out on a Sunday to help with a stubborn shower cartridge. I would recommend him to anyone needing plumbing help!
Courtney Jorgenson
Courtney Jorgenson
16:21 14 Jul 20
Very prompt, efficient, polite, and professional. Knowledgeable of needs and recommendations fit my circumstances. Thanks!
Nathan Mozingo
Nathan Mozingo
18:02 13 Jul 20
Master Tech replaced my ac/heating unit a couple of years ago and we have been very pleased with the follow-up checkup services we receive. Always very professional!
Joanne Nelson
Joanne Nelson
19:57 10 Jul 20
Tyson was very helpful and gave us advice for the future on how to save a little money with a project. We were very happy with him and his advice.
Wesley Dahms
Wesley Dahms
19:17 10 Jul 20
Josh Burleson installed our Home Depot purchased water softener. He was on time for the appointment, very professional and addressed all our questions. He was very neat in his work and cleanup. We would highly recommend calling MasterTech and Josh for all your needs.
Bette Everman
Bette Everman
22:48 29 Jun 20
Professional, personable and informative! I am on their yearly Check-Up plan for heating and cooling. Great price for a GREAT service.
Dorsey Ragland
Dorsey Ragland
17:55 29 Jun 20
Devon W. was a pleasure to work with. Efficient, clean, knowledgeable. Happy to have me sit with him while he worked so I could ask random plumbing questions that have always intrigued me. Highly recommend this business and Devin!
Pete Goodman
Pete Goodman
19:17 18 Jun 20
Chad arrived promptly when I was notified he was in route to my house. He was very friendly and professional and keeping social distancing practices. He was able to give options to get the result I needed. The cost was lower than what I had in mind and was completed in about an hour.I felt bad for him because it was hot and humid today (about 90) and the issue was outside of the house in direct sun...I set up a patio umbrella to cast some shade on him while he worked.Thanks again Chad! I will be calling MasterTech Plumbing for any other plumbing issues that arise!
Alen Petty
Alen Petty
18:22 03 Jun 20
Isaac and Alex removed a dead snake from my AC unit. They were professional and kind with a great sense of humor given the situation. They checked everything out to ensure it ran correctly and gave me an upfront price. I was quite satisfied.
Katie Ensign
Katie Ensign
17:54 01 Jun 20
Josh was so awsome! I had a "simple" leak in my faucet. He got the parts from his truck and fixed it like new, which is saying a lot as this faucet is over 10 years old. Very knowledgeable and friendly!
Betsy Kuhn
Betsy Kuhn
22:24 28 May 20
We had a great experience with Mastertech Plumbing from the time we made the phone call to request service. Our plumber Tyson was friendly, knowledgeable & professional. I would highly recommend this company & him for any plumbing needs.
Jamie Hogan
Jamie Hogan
17:40 22 May 20
I had a clogged drain that needed professional assistance. MasterTech was able to get Devin out to my house to fix our issue in record time. Devin was great and very professional and made sure the issue was fixed, the work area was clean and that I was satisfied with his work before he left. I highly recommend MasterTech.
Jeffery James
Jeffery James
17:01 08 May 20
When I called, the phone was answered by a pleasant service representative that remembered me and was understanding to my immediate need. MasterTech Plumbing tech Chad was very professional and friendly. He kept me informed of all what was wrong and didn’t try to up sell anything. I really appreciate Chad’s skillful knowledge. The quality of his work is exceptional. I know I can rely on Chad and MasterTech Plumbing.
Angela Hernandez
Angela Hernandez
02:12 08 Apr 20
The service we received today was awesome! Punctual, efficient, and up front and honest about prices and what products that we needed. Excellent work.
Cole Stoecklein
Cole Stoecklein
14:52 18 Mar 20
Josh is great! He is the one who usually comes to our house. He installed an overhead tank toilet, which is a tricky and time-consuming job. He overcame many obstacles and stuck with it until the job was completed and done right. Price was also good. MasterTech has always taken care of all our needs in a prompt and professional manner. Emergency service has always been rapid too.
Michael Lewis
Michael Lewis
17:24 11 Mar 20
Chris was great. Dispatch was great. We were scheduled quickly. Prices were very competitive. Edit: We had great success having our pipes fixed. Due to Missouri weather things were touch and go but Master Tech sure delivered! We are so please with the fix, financing and friendliness Master tech and our technician Chris Gilpin provided us. Will forever and always us Master tech. Certainly mighty nice people
Kimberly Threatt
Kimberly Threatt
01:30 29 Feb 20
We had to have emergency service today, Saturday. A serviceman was here in less than an hour. The repairs were made quickly, the charge was not over the top, even though it was not a work day, and the individual was friendly and courteous. We have learned to expect this kind of service from Master Tech. Thank you.
Barbara Timbrook
Barbara Timbrook
03:48 26 Jan 20
I recommend MasterTech. They show up when they tell you they will show up. They provide a comprehensive estimate and also a good explanation of the work that need to be done. Their work is good quality. They usually have the needed parts on their truck so they can do the task in a timely manner. They clean up the work area after the job is finished,
Dennis Catlett
Dennis Catlett
22:15 23 Jan 20
A great experience. First, on time, service tech was sent out when promised. Second, quick assessment of the problem (faulty sump pump). The tech not only quickly replaced the pump, but he made an alteration that will make it easier whenever a replacement has to be made. Bottom line, a most professional service. Certainly would recommend Master Tech to folks needing their service.
W B Tichenor
W B Tichenor
16:08 31 Dec 19
MasterTech is so great to work with. They're quick, clean, do great work, and have fair pricing. But the best thing about MasterTech is their people. Whoever is responsible for their human resources does a terrific job of selecting and/or training them. They're so friendly and provide excellent information and customer service. I highly recommend MasterTech!
Jason Black
Jason Black
20:37 26 Dec 19
Previously I had not been impressed with master tech. However, their technician Dillon not only fixed my emergency pipe break at 1am on a holiday but also saved me as a customer. This was the best service I have ever had at my home. He arrived promptly at 1am. Provided a couple of options on how to fix my problem both in the short and long term and quickly made repairs. He also has provided advice on how to address issues related to the water damage caused by the busted pipe. This was one of the most positive bad situation we have had as homeowners. Thank you Dillon and mastertech.
Michael Grote
Michael Grote
20:35 26 Dec 19
I had to change my appointment at the last minute and they were able to accommodate my new availability without any hesitation. My tech was really professional (Dillion). I got a call and a text to let me know he was on the way. He fixed my problem quickly and was so friendly. This is the second time that I have had to use a plumber and I will use Master Tech again since I have an old house with old plumbing.
Leigh Burton
Leigh Burton
14:01 22 Nov 19
HVAC and plumbing under one roof, what else do you need?! Great team!
CJ Roe
CJ Roe
01:06 30 May 18

Recent Posts

columbia plumber, columbia air conditioner, columbia hvac, air conditioner running

What is a Heat Pump, and How Does it Work?

Enjoying the summertime looks a little different right now (thanks COVID-19), but what probably won’t change is the summer heat. That means most of us are already looking for ways to keep cool while keeping our costs down. You know the usual suspects: AC units, window units, and ceiling fans. There’s also, you know, praying for the heat wave to break.

Scroll to Top