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Why Does My Home’s Water Temperature Keep Changing?


One moment it’s hot, then the next it’s cold — why can’t the water temperature be just right? As plumbers, we know how frustrating it is to deal with fluctuating water temperatures in your home. Drastic temperature changes can even be dangerous, especially if your water suddenly becomes hot without warning.

Getting to the bottom of this issue will require a bit of troubleshooting. Walking through the steps below will help you determine what is causing the water temperature fluctuation in your home.

If you are in need of water heater services in New Orleans or Metairie, contact Stuart Services today!

1. The water in my home gets hot suddenly.

If you’re having a problem with cold water, skip down to Step 2.

If the water in your home gets hot suddenly, try to notice when this occurs. Typically, this problem happens in the shower in an older home when someone flushes the toilet or turns on the bathroom faucet.

Why does this happen? Frequently in older homes, all the plumbing fixtures in one bathroom share the same central cold water line and hot water line. When you shower, you most likely use water from the cold line and the hot line so that what comes out is warm but not scalding. When someone turns on the faucet or flushes the toilet, suddenly, a bunch of cold water pressure is taken away from your shower, and you’re left with a lot of undiluted hot water coming out of the showerhead — ouch!

What should I do about it? Eventually, you can add more water lines when you get your home repiped. However, if you’re not ready to repipe, have a plumber install a thermostatic mixing valve in your shower. This device will prevent you from getting scalded when there’s a drop in cold water pressure.

2. The water in my home gets cold suddenly.

If your water goes from hot to cold then hot again, or from cold to hot then cold again, skip to Step 3.

If your water starts out hot and then gets cold, you most likely have a water heater issue.

Why does this happen? Routinely running out of hot water most likely means one of two things: Either your water heater is on its way out or your water heater isn’t big enough for your household. Tank water heaters last about 10 years on average, while tankless models last 20 years or more.

If your water heater is not old and you’re running out of hot water, then you may need to invest in a larger-capacity model. If you own a tank model, it’s possible that the tank size isn’t large enough to store all of the hot water your household needs. If you own a tankless model, you might be using too many hot water sources at once, overstretching the unit’s max flow rate (gallon per minute).

What should I do about it? If your water heater is 10 years or older, then replacing it will most likely solve the issue. However, it’s best to get a plumber’s professional opinion first. If your water heater is not that old and you don’t want to replace it with something with a higher capacity, you can try installing faucets and showerheads with low-flow rates. That way each shower that your family takes will use less hot water. If you own a tankless model, you can also try to avoid using hot water in too many places simultaneously.

tankless water heater temperature changing

3. The water in my home changes between hot and cold inconsistently.

If your water goes from hot to cold then hot again, or from cold to hot then cold again, you most likely have a problem with a thermostatic mixing valve in one of your plumbing fixtures (like your shower or one of your faucets). Thermostatic mixing valves are supposed to keep your water temperature consistent by detecting drops in hot and cold water pressure. When they stop working, you can experience extremely hot and cold water temperatures without even touching your faucet handles.

Why does this happen? Just like any device, thermostatic mixing valves get wear and tear after years of usage.

What should I do about it? Unless you’re a professional plumber, we don’t recommend repairing or replacing a thermostatic mixing valve yourself. This device needs to function correctly to prevent you from getting scalded. It’s safer to let a trained plumber replace this part.

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Need a hand with your home’s plumbing? Trust the New Orleans home experts at Stuart Services! Give us a call at 504-321-2079 today to schedule your service!