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Why Does My Tankless Water Heater Turn Cold Mid-Shower?

Everett Tankless Water Heater Cold

Many homeowners experience “cold water sandwich” problems with tankless systems. While the issue can be annoying, the good news is that there are clear reasons behind it and reliable, effective solutions to get your hot water flowing consistently again.

At 2 Sons Plumbing and Sewer, we’ve helped countless families in Everett troubleshoot and repair tankless water heater problems. Whether it’s something small like a cleaning issue or a bigger issue requiring a valve repair, our licensed plumbers know how to fix tankless water heaters and get your hot water flowing again.

Common Reasons Tankless Water Heaters Go Cold

Tankless systems work differently than traditional tanks, because they heat water on demand. But that means when something disrupts the flow or heating process, you’ll feel it right away. Here are the most common causes we see in Everett homes:

Low Water Flow

Tankless heaters need a certain level of flow to stay engaged. If the flow dips too low—say when someone flushes a toilet or runs another faucet—the burner can shut off, sending cold water your way.

Mineral Scale Buildup

Everett Water Heater Repair

Everett’s water often contains minerals like calcium and magnesium. Over time, these build up inside the unit, coating heating elements and reducing efficiency. This can lead to fluctuating temperatures and shorter bursts of hot water.

Mixing Valve Issues

Many systems use a mixing valve to blend hot and cold water safely. If the valve is out of balance or failing, it can send unexpected blasts of cold water right into your shower.

DIY Steps You Can Try

If your tankless water heater is turning cold mid-shower, here are a few simple things to try before calling for help:

  • Run another faucet – Increasing water flow helps keep the burner engaged.
  • Check the thermostat – Make sure the temperature is set to about 120°F for steady performance.
  • Descale the heater – Flushing the system once a year removes mineral deposits and keeps water moving smoothly.

These steps may fix minor issues, but if the problem keeps happening, it’s time for a professional inspection.

When to Call a Plumber in Everett

Everett Tankless Water Heater

Some warning signs mean it’s best to shut the system down and get expert help right away:

  • Error codes on the display screen
  • A gas smell near the unit
  • Frequent cold water bursts despite cleaning and adjustments
  • Water that never heats up at all

At 2 Sons Plumbing and Sewer, we use specialized tools to diagnose and fix tankless water heater problems. From descaling ($250–$500) to repairing or replacing valves, we’ll find the right solution to restore reliable hot water for your family.

Reliable Tankless Water Heater Repair in Everett

Cold showers are no fun, and with a properly working tankless water heater, you shouldn’t have to deal with them. Whether the issue is as simple as mineral buildup or as complex as a failing valve, our licensed plumbers know how to pinpoint the cause and fix it for good.

Call us today at (206) 487-1757 if your tankless water heater is running cold mid-shower. We’ll respond quickly, restore your hot water, and give you peace of mind knowing your system is in expert hands.

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Jennifer Suemnicht profile picture
Jennifer Suemnicht
2 months ago
I asked some of my real estate colleagues who people have been using for plumbing repairs lately and several said “2 Sons”! So friendly and responsive. Came out right away for an estimate, had the best follow up, came in with the best price, and got me on the schedule and got the work done on the very next day! Everyone I spoke with was friendly and fantastic! Highly recommend!
Jennifer Suemnicht profile picture
Jennifer Suemnicht
2 months ago
I asked some of my real estate colleagues who people have been using for plumbing repairs lately and several said “2 Sons”! So friendly and responsive. Came out right away for an estimate, had the best follow up, came in with the best price, and got me on the schedule and got the work done on the very next day! Everyone I spoke with was friendly and fantastic! Highly recommend!
Katy Garner profile picture
Katy Garner
3 months ago
We had a mystery leak per our meter reading. Riley and Riley saved the day. They promptly discovered the issue, resolved and repaired our pipes in one service call. They were quick, thorough and entirely delightful. They took the time to talk me through the job. I felt heard, safe and comfortable with the two of them in my house. For my next plumbing disaster I hope to get ‘The Riley’s’; but know, whoever comes will be excellent. Thanks 2 Sons!
Katy Garner profile picture
Katy Garner
3 months ago
We had a mystery leak per our meter reading. Riley and Riley saved the day. They promptly discovered the issue, resolved and repaired our pipes in one service call. They were quick, thorough and entirely delightful. They took the time to talk me through the job. I felt heard, safe and comfortable with the two of them in my house. For my next plumbing disaster I hope to get ‘The Riley’s’; but know, whoever comes will be excellent. Thanks 2 Sons!
Aaron Sutter profile picture
Aaron Sutter
3 months ago
2 Sons are my go to plumbers and I recommend them to friends and family looking for a recommendation.
2 Sons had my tenant's water heater replaced in the same day I called them! Justin and his apprentice were awesome! This wasn't a "quick" replacement in the garage - they had to figure out how to squeeze in the water heater through a tight crawl space on their hands and knees under furnace ducting.
Justin was knowledgeable and helpful in troubleshooting different replacement scenarios. He was kind and patient with my number of questions. He never once complained to me about the undesirable placement of the water heater under the house. My tenant even commented to me how kind Justin was to her.
Thank you for making this a quick and easy fix!
Aaron Sutter profile picture
Aaron Sutter
3 months ago
2 Sons are my go to plumbers and I recommend them to friends and family looking for a recommendation.
2 Sons had my tenant's water heater replaced in the same day I called them! Justin and his apprentice were awesome! This wasn't a "quick" replacement in the garage - they had to figure out how to squeeze in the water heater through a tight crawl space on their hands and knees under furnace ducting.
Justin was knowledgeable and helpful in troubleshooting different replacement scenarios. He was kind and patient with my number of questions. He never once complained to me about the undesirable placement of the water heater under the house. My tenant even commented to me how kind Justin was to her.
Thank you for making this a quick and easy fix!
Oksana Naidu profile picture
Oksana Naidu
4 months ago
Highly recommend 2 Sons. We had a leak in the master bath due to some malfunctioning fixtures and needed to install shut off valves on the hot and cold water lines to prevent further leaks while we waited on the faulty part replacements to be delivered. It was a treat to work with a professional and honest plumbing company that also does quality work. A great experience from first call to post-completion follow ups. Marcos, who was assigned to our job, was just awesome - thorough, efficient, knowledgeable, professional, courteous and helpful. He took his time to fully assess the issue, provided great options and then quickly repaired the problem. Thanks so much for great service in a stressful situation.
Oksana Naidu profile picture
Oksana Naidu
4 months ago
Highly recommend 2 Sons. We had a leak in the master bath due to some malfunctioning fixtures and needed to install shut off valves on the hot and cold water lines to prevent further leaks while we waited on the faulty part replacements to be delivered. It was a treat to work with a professional and honest plumbing company that also does quality work. A great experience from first call to post-completion follow ups. Marcos, who was assigned to our job, was just awesome - thorough, efficient, knowledgeable, professional, courteous and helpful. He took his time to fully assess the issue, provided great options and then quickly repaired the problem. Thanks so much for great service in a stressful situation.
Happy Lemon profile picture
Happy Lemon
4 months ago
We had an outstanding experience with this company! They provided incredibly fast, careful, and professional service for our commercial business. From start to finish, their customer service was absolutely excellent-responsive, friendly, and truly attentive to our needs.

A special thank you to our technician, ADAM, who did an exceptional job fixing our clogged hand sink. He was knowledgeable, efficient, and extremely professional & polite. He quickly resolved it with great skill and attention to detail.

Highly recommended!
Happy Lemon profile picture
Happy Lemon
4 months ago
We had an outstanding experience with this company! They provided incredibly fast, careful, and professional service for our commercial business. From start to finish, their customer service was absolutely excellent-responsive, friendly, and truly attentive to our needs.

A special thank you to our technician, ADAM, who did an exceptional job fixing our clogged hand sink. He was knowledgeable, efficient, and extremely professional & polite. He quickly resolved it with great skill and attention to detail.

Highly recommended!
Louisa profile picture
Louisa
4 months ago
Trung our tech and his apprentice Cole did a fantastic job yesterday. They worked tirelessly to replace our old CPVC pipes, install our new shower, and replace our kitchen sink. The job had a multitude of delays due our pipes not being plumb and some extra wall demo. They worked for at least 13+ hours yesterday and left our home at 11 pm. Trung wanted to ensure that we didn't have our water off longer than necessary. We could not be more thankful and grateful for their efforts in the rough in for our bathroom remodel. We look forward to having them back to install the shower/ tub combo, new bathroom faucet, and new toilet with a bidet seat. Trung always went out of his way to explain what was going on and helped us make informed decisions about our home. This is our 3rd or 4th time using 2 Sons and we couldn't recommend them more!

Update: Trung was extremely great with the final install! Unfortunately, there was a few mishaps with not communicating the right color of the shower/ tub combo and the hole for the toilet pipe not being wide enough for the toilet flange. Trung really went above and beyond to ensure we got the right parts and to cut the tile as best he could for the toilet to fit. He even had to double check our toilet because he thought he heard a leak. He even was able to replace our drain stopper and recommended a solution for making the tub drain match!
Louisa profile picture
Louisa
4 months ago
Trung our tech and his apprentice Cole did a fantastic job yesterday. They worked tirelessly to replace our old CPVC pipes, install our new shower, and replace our kitchen sink. The job had a multitude of delays due our pipes not being plumb and some extra wall demo. They worked for at least 13+ hours yesterday and left our home at 11 pm. Trung wanted to ensure that we didn't have our water off longer than necessary. We could not be more thankful and grateful for their efforts in the rough in for our bathroom remodel. We look forward to having them back to install the shower/ tub combo, new bathroom faucet, and new toilet with a bidet seat. Trung always went out of his way to explain what was going on and helped us make informed decisions about our home. This is our 3rd or 4th time using 2 Sons and we couldn't recommend them more!

Update: Trung was extremely great with the final install! Unfortunately, there was a few mishaps with not communicating the right color of the shower/ tub combo and the hole for the toilet pipe not being wide enough for the toilet flange. Trung really went above and beyond to ensure we got the right parts and to cut the tile as best he could for the toilet to fit. He even had to double check our toilet because he thought he heard a leak. He even was able to replace our drain stopper and recommended a solution for making the tub drain match!
Kathy Cook profile picture
Kathy Cook
4 months ago
I have to say Bob was amazing!!! I had a clogged drain in my kitchen sink. Bob came in and took every precaution to be neat & clean. He explained to me what he was going to do and gave me the pricing and I agreed and he got to work. He was super kind and polite and fixed my drain issue. He was a pleasure to work with. I would highly recommend using 2 Sons!
Kathy Cook profile picture
Kathy Cook
4 months ago
I have to say Bob was amazing!!! I had a clogged drain in my kitchen sink. Bob came in and took every precaution to be neat & clean. He explained to me what he was going to do and gave me the pricing and I agreed and he got to work. He was super kind and polite and fixed my drain issue. He was a pleasure to work with. I would highly recommend using 2 Sons!
Emily Speakman profile picture
Emily Speakman
4 months ago
Had issues at home with water backup. Dave was prompt, professional, and genuinely kind. He communicated between myself and my landlord, explaining the issues and next steps. He quickly put an interim solution in place and outlined the long-term needs. Felt super reliable and easy to work with — highly recommend 2 Sons Plumbing.
Emily Speakman profile picture
Emily Speakman
4 months ago
Had issues at home with water backup. Dave was prompt, professional, and genuinely kind. He communicated between myself and my landlord, explaining the issues and next steps. He quickly put an interim solution in place and outlined the long-term needs. Felt super reliable and easy to work with — highly recommend 2 Sons Plumbing.
Frank Church V profile picture
Frank Church V
4 months ago
We contacted these Plumbers on a Friday using Yelp quotes, and they were the fastest to reply and the fastest to engage with us when we had questions. We felt that warranted to give them the opportunity to give us the first consultation. Sometimes we get multiple consults if we get any icky feeling from the people doing it. We didn’t feel that way with this company.

Our toilet was leaking, and we expected we probably could use a new one. But wanted a professional estimate and options.

We got hooked up with their team to schedule it and they were able to give us a time only a day out. We asked for a 8-1pm window and received automated text and a formal phone call from a dispatcher saying how far out the plumber technician was.

The plumber who showed up was named Carey. We also a received a picture of him before he arrived for safety concerns which I thought was a good touch of care from the company. Carey was lights-out the best guy we could have asked for.

He showed up within the approximate eta and was kind, gracious, considerate of our space and gave us a myriad of options. He quoted us prices that felt quite fair, and we chose the option where he removes the toilet and chooses a toilet for us: though we talked about the various options beforehand.
All and all he left for 30 min to get the toilet: and returned to install it. Installation was complete within another 30 minutes.

He was so good man. And we just felt like this is how service and care and things should be in this world. It’s always refreshing when you get that. Because so many outfits just: make you regret everything.

The work was quick, professional, and he was happy to be there and gave us information every step of the way that we respected and appreciated.

We will use this company in the future. You earned our respect and business.
Frank Church V profile picture
Frank Church V
4 months ago
We contacted these Plumbers on a Friday using Yelp quotes, and they were the fastest to reply and the fastest to engage with us when we had questions. We felt that warranted to give them the opportunity to give us the first consultation. Sometimes we get multiple consults if we get any icky feeling from the people doing it. We didn’t feel that way with this company.

Our toilet was leaking, and we expected we probably could use a new one. But wanted a professional estimate and options.

We got hooked up with their team to schedule it and they were able to give us a time only a day out. We asked for a 8-1pm window and received automated text and a formal phone call from a dispatcher saying how far out the plumber technician was.

The plumber who showed up was named Carey. We also a received a picture of him before he arrived for safety concerns which I thought was a good touch of care from the company. Carey was lights-out the best guy we could have asked for.

He showed up within the approximate eta and was kind, gracious, considerate of our space and gave us a myriad of options. He quoted us prices that felt quite fair, and we chose the option where he removes the toilet and chooses a toilet for us: though we talked about the various options beforehand.
All and all he left for 30 min to get the toilet: and returned to install it. Installation was complete within another 30 minutes.

He was so good man. And we just felt like this is how service and care and things should be in this world. It’s always refreshing when you get that. Because so many outfits just: make you regret everything.

The work was quick, professional, and he was happy to be there and gave us information every step of the way that we respected and appreciated.

We will use this company in the future. You earned our respect and business.
Sitong Liu profile picture
Sitong Liu
4 months ago
I initially hired this company to address a leak in my water service line. Due to repeated misdiagnosis and unsuccessful repair attempts, the work ultimately escalated into a full water service line replacement, resulting in a final cost far higher than what I had initially expected. While the replacement is now completed and functioning, the overall experience was frustrating and poorly managed.

From the start, pricing and expectations were unclear. I was told repair costs couldn’t be determined until excavation, yet on the day of work—before anything began—I was asked to sign for a high fixed repair price based on assumptions that were never discussed during the estimate.

The first repair attempt failed, and the leak clearly continued. No further investigation was done, I was required to pay in full, and I was told a discount would only apply if I committed to a full water service line replacement the same day, before the issue was properly resolved.

After paying for a second leak detection myself, the original leak was confirmed to still be present. Management involvement was requested but delayed, and during a follow-up visit I was asked to sign a new agreement stating the work was only a “repair attempt” with no warranty, despite the original repair being sold as warrantied.

I later proceeded with the water service line replacement based on specific assurances about the final cost, but the estimate I received did not align with those assurances. Throughout the process, I had to make multiple phone calls and send repeated emails over several days just to get responses.

While the final replacement works, the lack of technical competence, shifting pricing and warranty terms, and consistently poor communication made this an unnecessarily stressful experience. I would not use this company again.
Sitong Liu profile picture
Sitong Liu
4 months ago
I initially hired this company to address a leak in my water service line. Due to repeated misdiagnosis and unsuccessful repair attempts, the work ultimately escalated into a full water service line replacement, resulting in a final cost far higher than what I had initially expected. While the replacement is now completed and functioning, the overall experience was frustrating and poorly managed.

From the start, pricing and expectations were unclear. I was told repair costs couldn’t be determined until excavation, yet on the day of work—before anything began—I was asked to sign for a high fixed repair price based on assumptions that were never discussed during the estimate.

The first repair attempt failed, and the leak clearly continued. No further investigation was done, I was required to pay in full, and I was told a discount would only apply if I committed to a full water service line replacement the same day, before the issue was properly resolved.

After paying for a second leak detection myself, the original leak was confirmed to still be present. Management involvement was requested but delayed, and during a follow-up visit I was asked to sign a new agreement stating the work was only a “repair attempt” with no warranty, despite the original repair being sold as warrantied.

I later proceeded with the water service line replacement based on specific assurances about the final cost, but the estimate I received did not align with those assurances. Throughout the process, I had to make multiple phone calls and send repeated emails over several days just to get responses.

While the final replacement works, the lack of technical competence, shifting pricing and warranty terms, and consistently poor communication made this an unnecessarily stressful experience. I would not use this company again.

Services Provided:

SEWER :

BASEMENT DRAIN OVERFLOW

BASEMENT FLOODING

BLOCKED SEWER PIPE

BLUELIGHT SEWER REPAIR

BROKEN PIPES

BROKEN WATER LINE

BURST PIPE HELP

CAMERA PIPE INSPECTION

CHEMICAL DRAIN CLEANERS

CLOGGED DRAIN

CLOGGED MAINLINE SEWER

CLOGGED SEWER

CLOGGED SEWERS

CLOGGING DRAIN

COMMERCIAL DRAIN REPAIRS

DRAIN CLEANER

DRAIN CLEANING

DRAIN FIELDS

DRAIN LINE REPLACEMENT

DRAIN REPAIR

DRIPPING FAUCET

EMERGENCY SEWER SERVICE

EXCAVATION

FRENCH DRAINS

GARBAGE DISPOSAL NOISE

GURGLING DRAINS

HOT WATER RUNS OUT

HYDRO JETTING

HYDRO JETTING SEWERS

LOCATING SEWER LINE

LOW WATER PRESSURE FAUCET

MAINLINE REPLACEMENT

NEW TOILET INSTALLATION

PIPE BURSTING

PIPE LOCATOR

PIPE LOCATOR

REPAIR SEWER LINE

REPIPING COPPER VS PEX

REPLACE DRAIN LINE

REPLACING SEWERS

ROOTER

ROOTS IN SEWER

SEWAGE BACKUPS

SEWAGE GRINDER

SEWAGE LINE REPAIRS

SEWAGE PUMP

SEWER

SEWER BACKUP

SEWER BURST PIPES

SEWER CAMERA INSPECTION

SEWER CLEANOUT

SEWER CONTRACTOR

SEWER FINANCING

SEWER FINANCINGS

SEWER INSPECTION

SEWER INSTALLATION

SEWER JETTER

SEWER JETTING

SEWER LEAK DETECTION

SEWER LINE

SEWER LINE HELP

SEWER LINE INSPECTION

SEWER LINE INSTALL

SEWER LINE REPAIRS

SEWER LINE REPLACEMENT

SEWER LINE REPLACING

SEWER LINING

SEWER LOCATOR

SEWER MAIN LINE INSTALL

SEWER PIPE

SEWER PIPE BURSTING REPAIR

SEWER PIPE INSTALL

SEWER PIPE LINING

SEWER PIPE LOCATOR

SEWER PIPE REPAIR

SEWER PIPE REPLACEMENT

SEWER PUMP SERVICES

SEWER REPAIR

SEWER REPAIR NEAR ME

SEWER REPLACEMENT

SEWER ROOT ISSUE

SEWER SCOPE

SEWER SCOPING

SEWER TANK PUMPING

SHOWER DRAIN SMELLS

SLAB LEAK DETECTION

SLAB LEAK REPAIR

SNAKING TOILET

SUMP PUMP

SUMP PUMPS

TOILET

TOILET AUGER SERVICES

TOILET BACKUP

TOILET BASE LEAK

TOILET GURGLING

TOILET KEEP RUNNING

TOILET REPAIR

TOILET REPAIRS

TOILET REPLACEMENT

TOILETS

TRENCHLESS SEWER REPAIRS

TRENCHLESS SEWER REPLACEMENT

TRENCHLESS SEWERS

VIDEO PIPE INSPECTION

VIDEO PIPE INSPECTION

WATER LEAKING TOP

WATER HEATER PERMIT