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Tankless Water Heater Shuts off During Shower [FIXED]

For some, tankless water heaters are the wave of the future, creating hot water on demand while reducing energy bills and lasting longer than traditional tank units. But one major downside of tankless water heaters is their tendency to go cold during a shower.

The older generation of tankless water heaters would simply run out of hot water. While that issue still happens today, there are still other problems that can severely affect your bathroom rituals.

Nobody likes an unexpected cold shower, so this article will cover the reasons why your tankless water heater shuts off and provide you with information on how to prevent this problem. 

Let’s get started.

tankless water heater
Source: Curoso Plumbing

Why Does My Tankless Water Heater Keep Shutting Off?

Tankless Heater Hot Water Capacity

While tankless water heaters do not carry a specific capacity like a tank unit, they can only heat a certain amount of GPM (Gallons Per Minute).

If you’re running multiple appliances at once or taking a very long shower, it may seem like your unit turned off. But in actuality, you are using more hot water than your tankless heater can provide.

This is a very common issue that plagued early tankless water heaters and still persists today. This problem is especially common for those that just switched from a traditional water heater.

Temperature Fluctuation

Temperature fluctuations in your water supply can occur for a few reasons. Usually, what happens is there is still some hot water in your pipes from the last time the shower was used. You step into the shower, thinking you have a steady stream of hot water.

But once the hot water in your pipes runs out, you get some cold water because your heater hasn’t caught up yet. Then that cold water will be followed by a steady stream of hot water. This can give you the impression that your water heater is turning on and off.

Faulty Components

Tankless water heaters are a bit more complex than their traditional siblings. With additional components, there is a greater chance for something to go wrong.

Tankless water heaters have motherboards that can malfunction and sensors that can give out. Add this along with the traditional aspects of water heating like burners, fans, and thermostats.

If any one of these components fails to do its job, you will be left with a water heater that can turn off while you are using it, or it may not work at all.

Temperature Regulating Valves

Temperature regulating valves are connected to your plumbing and do not have the ability to communicate with your water heater. Therefore, your tankless heater may send out water at the right temperature, but a regulating valve changes the temperature somewhere along the way.

The regulating valve might be faulty or just not adjusted correctly. Your water valve might believe it’s saving you from scalding hot water when in fact, all you are getting is a cold shower.

How to Prevent Tankless Water Heater Shutting Off During Showers

Being Mindful of a Tankless Water Heaters Limits

Previously we discussed GPM or gallons per minute. For example, most showers consume between 3 to 4 gallons per minute, but most water heaters are only rated between 5 to 7 GPM.

This means that if you were to take a shower while someone was doing dishes or a load of laundry, you would run out of hot water. Unfortunately, besides taking a shower when no other appliances are running, there’s not much else you can do to prevent this issue.

Additionally, some tankless water heaters will turn off if they get overloaded, leaving your home without hot water for hours.

Preventing Fluctuation

The best way to prevent temperature fluctuations in your showers water is patience. First, make sure no one else in your home is using any hot water.

Then run your shower for a few minutes and wait before entering the shower. This will allow any cold water you would have been doused with to pass and will give your water heater some time to catch up.

This way, any temperature fluctuation you experience in the shower can be narrowed down to someone else flushing a toilet or using hot water.

Maintaining a Tankless Water Heaters Components

Once a year, you should do some maintenance on your tankless water heater to give it a long lifespan and prevent any issues.

Depending on your needs, this maintenance can be as simple as a visual inspection or as advanced as a complete vinegar flush of the system.

If you suspect one of your water heater’s components is acting up like the motherboard or sensor; you should consult the manufacturer. They will likely send a technician out to solve the problem, possibly free of charge if the issue is covered under warranty.

Inspecting or Adjusting Regulating Valves

Some homeowners buy a home without any knowledge of the temperature regulating valves or how they were adjusted. This is not a common issue but can possibly be the cause of your problem.

These valves have manual controls for adjusting the temperature of the water. You can try adjusting these valves to get the temperature you desire.

While you are adjusting these regulating valves, you have the opportunity to inspect them for any damage and determine whether or not they need to be replaced.

Adam McCoy

Adam is an HVAC expert and the owner of Mackydo's HVAC Services with decades of experience in fixing and installing air conditioning units, furnaces, and every type of cooling and heating equipment you can think of.

Adam believes that your home is your sanctuary. He loves sharing advice based on his lifelong experience and treats every HVAC problem as if it was his own.

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