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Why Does My Tankless Water Heater Sometimes Go Cold Mid-Shower?

You are in the middle of a shower, nice and comfortable, and then out of nowhere—the water goes freezing cold. Nothing ruins a morning faster. We hear this complaint a lot from Tacoma homeowners with tankless water heaters. The good news? Most of the time, it is not a sign your heater is done for. It is usually something simple, like low water flow or a little mineral buildup inside the system. At 2 Sons Plumbing Tacoma, we see it all the time and know how to get your hot water back on track.

Why Tankless Water Heaters Go Cold

When a tankless heater shuts off in the middle of a shower, a few common issues are usually to blame:

Not enough flow: Tankless heaters need a certain amount of water moving through them. If it drops, the burner shuts off.
Scale buildup: Minerals inside the unit can block sensors and slow everything down.
Settings off: If the temperature isn’t dialed in around 120°F, the system may not behave the way you expect.

Most of these are small problems that can be fixed without replacing the unit.

Quick Fixes You Can Try

A couple of simple steps may solve it:

Turn on another faucet. Adding flow can keep the system engaged.
Check the temperature. Make sure it’s set around 120°F—hot enough for comfort, safe enough for the system.
Flush the unit. Once a year, use a descaling kit to clear out mineral buildup.
Regular descaling makes a big difference—it keeps the heat steady and helps your unit last longer.

When to Call a Plumber

Sometimes the fixes above won’t cut it. Give 2 Sons Plumbing Tacoma a call at (206) 487-1757 if:

You see error codes on the display.
There’s a gas smell near the heater.
The water still cuts out even after flushing the system.

Those are signs of a bigger issue, like a failing valve or control board. That’s when you need professional tools and know-how.

What It Usually Costs

Here’s what most Tacoma homeowners can expect:

Descaling service: $250–$500
Valve or control repairs: Cost depends on the part and labor

Fixing things early almost always saves money compared to waiting until the unit stops working altogether.

Why Call Local Experts

Tankless water heaters are great—compact, efficient, endless hot water when they’re working right. But they’re also a little more sensitive than standard tanks. At 2 Sons Plumbing Tacoma, our plumbers work on them every week. We know the quirks, we know the brands, and we’ll explain the fix in plain language so you’re not left guessing.

Keep the Hot Water Coming

Don’t let cold surprises keep ruining your showers. Call 2 Sons Plumbing Tacoma at (206) 487-1757, and we’ll send a plumber who knows tankless systems inside and out.

One call and you can stop shivering, stop guessing, and get back to showers that stay hot from start to finish.

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