Why Does My Tankless Water Heater Go Cold in the Shower?
You’re standing in the shower, finally relaxing after a long day. The water feels just right—until suddenly, it turns ice cold. You jump back, frustrated, wondering why your tankless water heater keeps letting you down. At 2 Sons Plumbing and Sewer Seattle, we hear this story all the time. The idea of endless hot water sounds great, but when the system isn’t set up or maintained correctly, cold surprises can sneak in. The good news? Most fixes are easier than you think.
Why Tankless Water Heaters Sometimes Run Cold
If you’re getting hit with cold water mid-shower, these common culprits are usually to blame:
- Low water flow – Tankless heaters need strong flow to stay activated. If the water becomes too slow, the burner shuts off and you get a cold blast.
- Mixing valve issues – A faulty or worn valve may be blending in too much cold water.
- Mineral scale buildup – Seattle’s hard water can leave deposits inside the heater, slowing heating and causing inconsistent temperatures.
What You Can Try on Your Own
Before calling a plumber, try these easy fixes:
- Turn the handle up – Ensure enough flow for the heater to stay active.
- Set the temperature to around 120°F – This helps stabilize output and avoid fluctuations.
- Flush the unit yearly – Descaling prevents mineral buildup that cuts off heat.
If you’ve tried these steps and still get cold bursts, the issue likely requires a professional.
When to Bring in a Pro
Call a plumber right away if you notice:
- A gas smell near the heater
- Error codes flashing on the display
- Frequent cold swings even with normal flow and settings
These symptoms often indicate deeper issues that require safe handling and proper tools.
What It Usually Costs
Costs vary depending on the root cause, but most Seattle homeowners see:
- Routine descaling and flush: $250–$500
- Mixing valve service or replacement: Varies by brand and needed parts
Regular maintenance is the best way to avoid costly breakdowns—keeping scale under control helps your heater run smoothly and last longer.
Stop Putting Up with Cold Showers
If your tankless heater keeps cutting out, call 2 Sons Plumbing and Sewer Seattle at (206) 487-1757. We’ll send a plumber who works with tankless systems every day and knows exactly what to look for. Sometimes it’s a quick flush, sometimes a valve adjustment—but whatever the cause, we’ll track it down and get your hot water flowing again.
One call is all it takes. No more guessing. No more shivering halfway through your shower. Just steady, reliable hot water—exactly the way it should be.
Amber Rhodes
3 weeks ago
I had a great experience with 2 Sons Plumbing and Sewer. I scheduled an appointment online last night, and they called me first thing this morning. Natalie was so kind and even offered me an earlier appointment that same day, which I really appreciated.
Justin came out and was friendly, professional, and honest. He gave me a fair estimate for the repair I needed and also provided estimates for a few additional code-related fixes that may need to be addressed in the future. I never felt pressured to approve any extra work, which I really appreciated.
From scheduling to the service visit, the entire experience was easy and professional. I would definitely use 2 Sons Plumbing and Sewer again and would happily recommend them to others!
Justin came out and was friendly, professional, and honest. He gave me a fair estimate for the repair I needed and also provided estimates for a few additional code-related fixes that may need to be addressed in the future. I never felt pressured to approve any extra work, which I really appreciated.
From scheduling to the service visit, the entire experience was easy and professional. I would definitely use 2 Sons Plumbing and Sewer again and would happily recommend them to others!
Amber Rhodes
3 weeks ago
I had a great experience with 2 Sons Plumbing and Sewer. I scheduled an appointment online last night, and they called me first thing this morning. Natalie was so kind and even offered me an earlier appointment that same day, which I really appreciated.
Justin came out and was friendly, professional, and honest. He gave me a fair estimate for the repair I needed and also provided estimates for a few additional code-related fixes that may need to be addressed in the future. I never felt pressured to approve any extra work, which I really appreciated.
From scheduling to the service visit, the entire experience was easy and professional. I would definitely use 2 Sons Plumbing and Sewer again and would happily recommend them to others!
Justin came out and was friendly, professional, and honest. He gave me a fair estimate for the repair I needed and also provided estimates for a few additional code-related fixes that may need to be addressed in the future. I never felt pressured to approve any extra work, which I really appreciated.
From scheduling to the service visit, the entire experience was easy and professional. I would definitely use 2 Sons Plumbing and Sewer again and would happily recommend them to others!
Jackie Johanson
4 weeks ago
⭐⭐⭐⭐⭐
I had a project that required a quick turnaround for some temporary top-out plumbing, and Two Sons Plumbing was incredibly responsive from the start. They came out quickly to provide a quote and, even during what I know is their peak season, they prioritized getting my project scheduled. That level of customer service was greatly appreciated.
The quote was a bit of sticker shock, but that’s simply the reality of the Seattle market—not a reflection of their service. What really stood out was that the same person who came out to provide the estimate also completed the work. It meant I didn’t have to explain everything twice, and we’d already built a level of trust before the job even started.
The quality of the work was excellent, and they even went above and beyond by replacing a damaged toilet lid at no extra charge. Small gestures like that make a big difference.
If you’re looking for a fast, reliable plumbing company that does quality work and takes great care of its customers, I’d definitely recommend Two Sons Plumbing.
I had a project that required a quick turnaround for some temporary top-out plumbing, and Two Sons Plumbing was incredibly responsive from the start. They came out quickly to provide a quote and, even during what I know is their peak season, they prioritized getting my project scheduled. That level of customer service was greatly appreciated.
The quote was a bit of sticker shock, but that’s simply the reality of the Seattle market—not a reflection of their service. What really stood out was that the same person who came out to provide the estimate also completed the work. It meant I didn’t have to explain everything twice, and we’d already built a level of trust before the job even started.
The quality of the work was excellent, and they even went above and beyond by replacing a damaged toilet lid at no extra charge. Small gestures like that make a big difference.
If you’re looking for a fast, reliable plumbing company that does quality work and takes great care of its customers, I’d definitely recommend Two Sons Plumbing.
Jackie Johanson
4 weeks ago
⭐⭐⭐⭐⭐
I had a project that required a quick turnaround for some temporary top-out plumbing, and Two Sons Plumbing was incredibly responsive from the start. They came out quickly to provide a quote and, even during what I know is their peak season, they prioritized getting my project scheduled. That level of customer service was greatly appreciated.
The quote was a bit of sticker shock, but that’s simply the reality of the Seattle market—not a reflection of their service. What really stood out was that the same person who came out to provide the estimate also completed the work. It meant I didn’t have to explain everything twice, and we’d already built a level of trust before the job even started.
The quality of the work was excellent, and they even went above and beyond by replacing a damaged toilet lid at no extra charge. Small gestures like that make a big difference.
If you’re looking for a fast, reliable plumbing company that does quality work and takes great care of its customers, I’d definitely recommend Two Sons Plumbing.
I had a project that required a quick turnaround for some temporary top-out plumbing, and Two Sons Plumbing was incredibly responsive from the start. They came out quickly to provide a quote and, even during what I know is their peak season, they prioritized getting my project scheduled. That level of customer service was greatly appreciated.
The quote was a bit of sticker shock, but that’s simply the reality of the Seattle market—not a reflection of their service. What really stood out was that the same person who came out to provide the estimate also completed the work. It meant I didn’t have to explain everything twice, and we’d already built a level of trust before the job even started.
The quality of the work was excellent, and they even went above and beyond by replacing a damaged toilet lid at no extra charge. Small gestures like that make a big difference.
If you’re looking for a fast, reliable plumbing company that does quality work and takes great care of its customers, I’d definitely recommend Two Sons Plumbing.
Brad Poirier
2 months ago
Had a great experience with 2 Sons Plumbing and Sewer and the representative they sent, Jake. They did a fantastic job communicating through email, text, and calls, sending reminders when the appointment was and who their representative was, and when he would arrive. Jake did a wonderful job hunting done where the leak was coming from and explaining the options I had for getting the leak repaired. When he left he emailed my receipt, pictures he had taken of my water lines under the house, and the options I could use to compete locating and repairing the leak. Highly recommend them. A very professional outfit.
Brad Poirier
2 months ago
Had a great experience with 2 Sons Plumbing and Sewer and the representative they sent, Jake. They did a fantastic job communicating through email, text, and calls, sending reminders when the appointment was and who their representative was, and when he would arrive. Jake did a wonderful job hunting done where the leak was coming from and explaining the options I had for getting the leak repaired. When he left he emailed my receipt, pictures he had taken of my water lines under the house, and the options I could use to compete locating and repairing the leak. Highly recommend them. A very professional outfit.
Jennifer Suemnicht
3 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
3 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
5 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
5 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
5 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!
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
5 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!
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
5 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
5 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
5 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!
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
5 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!
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
5 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!
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
5 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!
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
5 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
5 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!