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Areas We Serve

Why Does My Tankless Water Heater Sometimes Turn Cold?

You’re in the shower, enjoying steady hot water—when suddenly the temperature drops, and you’re hit with a blast of cold. For many Federal Way homeowners, this “cold water sandwich” effect is a common frustration. The good news? It usually points to issues that can be identified and fixed.

At 2 Sons Plumbing Federal Way, we’ve helped countless families restore reliable hot water. Our licensed plumbers know the ins and outs of tankless water heater systems, and we’re here to explain what’s happening, why it occurs, and what you can do about it.

Common Reasons Tankless Water Heaters Run Cold

When your tankless water heater cuts out unexpectedly, it often comes down to one of these issues:

Not enough water flow – Tankless units need a minimum flow rate to fire up. If the faucet or shower isn’t running enough water, the system can shut off mid-use.
Scale buildup – Minerals in Federal Way’s water supply can accumulate inside the unit, blocking heat exchange and reducing performance.
Temperature mixing – If multiple fixtures are in use or the thermostat is set incorrectly, cold water can sneak into the line.

DIY Steps You Can Try

Before calling for professional help, try these simple checks:

Run another faucet – Boosting flow may help the unit maintain consistent heating.
Check the thermostat – Make sure your unit is set to at least 120°F for safe, reliable performance.
Flush and descale annually – Hard water minerals can build up quickly. A regular flush helps your system run smoothly.

When to Call a Professional

While minor hiccups can sometimes be resolved at home, call a licensed plumber if you notice:

A gas odor near the unit
Error codes on the display screen
Repeated shutdowns even after basic troubleshooting

Tankless water heaters are advanced systems. Attempting to repair gas or electrical components without training can be dangerous and worsen the problem. Our experienced team has the right tools and knowledge to safely diagnose the issue.

What It Might Cost

The cost depends on the issue, but here’s a general guide for Federal Way homeowners:

Descaling service: $250–$500
Valve or component replacement: Varies depending on part and brand

At 2 Sons Plumbing Federal Way, we believe in transparency. We’ll walk you through the problem, explain your options in plain language, and give you upfront pricing so there are no surprises.

Restore Your Hot Water Comfort with 2 Sons Plumbing Federal Way

Losing hot water in the middle of a shower or chore is more than just an inconvenience—it disrupts your day and your comfort.

At 2 Sons Plumbing Federal Way, we’ve built our reputation on fast response times, honest communication, and quality repairs you can trust. Call us today at (206) 487-1757. With 2 Sons Plumbing Federal Way, you’ll get expert service, clear answers, and the peace of mind that your hot water is back to running exactly how it should.

2 Sons Plumbing, Electrical, Heating & Air

4.9

Based on 3393 reviews

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Maria Kute

23:01 18 Nov 25

Thank you, Bob, for your professional, courteous, and kind service! My downstairs tub was running with high pressure due to some worn out stems. Bob was thorough—but unfortunately our fixtures are quite old, and he didn’t have appropriate replacements available the first day. However, they were able to find the appropriate stems for our tub and fixed the leak right away day 2. I cannot speak highly enough about how grateful I am for the way 2 Sons accommodated my schedule when they needed to return with the appropriate fixtures. The technician was a genuine joy to work with—and I appreciate the quick follow up and turn around. I also appreciate the way Bob walked me through the process and double checked for leaks.

Maria Kute

23:01 18 Nov 25

Evan Rose

16:17 18 Nov 25

We had a great experience. Brandon and Chris were very polite and professional. We had a massive leak under a toilet and they came and fixed it on a Saturday. They were very timely and hardworking. Ethan was another who was also very polite and professional. Pricing was also very manageable for the extent of the problem we had. I would highly recommend.

Evan Rose

16:17 18 Nov 25

YuliyaG

22:06 14 Nov 25

I had a great experience with 2Sons Plumbing. Communication was on point from start to finish. Dave arrived on time, was very friendly, and knowledgeable. He also gave me a helpful heads-up about our heater and offered great advice. I really appreciate the professionalism and will definitely use them again!

YuliyaG

22:06 14 Nov 25

Brandy Przybylak

19:28 05 Nov 25

We really enjoyed our experience with 2 Sons. We had an emergency that had water all over our kitchen and basement. They were able to send someone out later in the evening for us after several other companies either cancelled on us or said they couldn't come until the next day. Our technician/plumber Riley was great to work with - friendly, quick, and effective! They even gave us a call back a few days later to check in on our experience and to answer some extra questions we had. Highly recommend!

Brandy Przybylak

19:28 05 Nov 25

Carol Wong

19:21 04 Nov 25

I have not decided to go with 2 Sons for the plumbing issues I have yet. However, I am very impressed by the technician, Guy, who came for the appointment. He was professional, friendly, knowledgeable, courteous, and thorough. I told him that I was just getting a quote and not ready to commit to do the repair right away. He was very understanding. I have a clogged kitchen sink, disconnected washer hose causing water damage, and likely a disconnected pipe behind the wall. He explained the steps I need to take before he can help for all three issues. Like I should hire the restoration company to repair the water damage before reconnecting the pipes. He also helped to take pictures and referred me to a restoration company for the jobs outside of his scope. Before he left, he measured the water pressure to make sure the pressure is within a normal range. Just to make sure the water is not putting too much pressure on the fixtures resulting leaks. It was definitely a surprisingly pleasant and thorough experience with Guy.

Carol Wong

19:21 04 Nov 25

Joanne Chan

01:00 31 Oct 25

Excellent service from 2 Sons Plumbing – highly recommended!

We recently had 2 Sons Plumbing come out to fix several issues at our place. We couldn’t be happier with the results. Marcos and Chris were absolutely fantastic — professional, knowledgeable, and very thorough in their work. Every single job was done with precision and care.

Marcos and Chris took the time to explain what they were doing, answered all our questions patiently, and made sure everything was up to code and functioning perfectly before they left. They worked efficiently, left the area spotless.

It’s rare to find such reliable, honest, and detail-oriented professionals these days. I wouldn’t hesitate to recommend them to my friends and neighbors.

Joanne Chan

01:00 31 Oct 25

Jurusha Emerson

16:11 28 Oct 25

I called 2 Sons Plumbing and was able to get them to come out to the house the very next day. The over the phone customer service were very personable and friendly. On the day of my appointment, Bob was the one sent to our house to fix our kitchen faucet. Bob was extremely friendly and helpful in fixing my faucet. He was very considerate and quick with his work. I did not feel like I was being taken advantage of or overpriced as far as how much they were charging. Bob was always transparent with the cost and also trying to find the most cost-effective way to accomplish what needed to get done? I would recommend 2 Sons plumbing to anyone who needs plumbing service. 2 Sons plumbing has a gem for an employee (Bob). If I were to call 2 Sons plumbing again for service, I would definitely want to request Bob as my priority person.
Thankyou so much

Jurusha Emerson

16:11 28 Oct 25

Mackenzie Maynes

02:22 28 Oct 25

After the recent power outage I discovered that my combi-boiler went on the fritz, meaning no hot water and no heat in my home—a very chilly situation for Seattle fall. 2 Son’s was so friendly and able to send out Adam same-day which was a huge relief! Adam quickly assed the issue, fixed it and provided a thorough explanation of what he did to get the system up and running again (which I deeply appreciated). I am thoroughly impressed by his knowledge of these units; turns out the pressure reducing valve on my machine also needs to be replaced, which explains why my water pressure has always been a bit funky between hot and cold. Adam provided an affordable proposal for a future repair to my unit for optimal functioning. Would absolutely recommend Adam and 2 Sons!

Mackenzie Maynes

02:22 28 Oct 25

Amy J

01:15 28 Oct 25

Had a great experience with 2 Sons Plumbing, Heating & Air. Their scheduling system was smooth — I got a call when Carey was assigned, could track his arrival, and everything ran on time. Carey was fantastic! He inspected the garbage disposal, coordinated with my property manager for approval, and quickly installed the new system. He was respectful, efficient, and made sure everything worked perfectly. Really appreciated his help!

Amy J

01:15 28 Oct 25

Oaktree President

22:17 24 Oct 25

Our house decided to replace our own toilet, but we got stuck halfway through because we didn’t have the right tools and accidentally broke an anchor bolt. I called 2 Sons Plumbing, and they showed up within an hour to help us out. Derek, our plumber, was super friendly, explained everything clearly, and got the job done quickly and professionally. Excellent service all around—highly recommend!

Oaktree President

22:17 24 Oct 25