Why Does Flushing The Toilet Affect The Shower?

Toilet Flush Affecting Shower

If you’re enjoying a relaxing shower, suddenly getting blasted with scalding hot water can be a painful shock. But, when other members of the household flush the toilet while you’re showering, that’s exactly what happens. Plus, you might even end up with less water flowing from the showerhead.

When someone flushes the toilet while you’re showering, the toilet needs water to refill the tank. Toilets use cold water, so it pulls the cold water from your shower, resulting in a sudden increase in hot water. While the toilet uses this water to refill the toilet tank, it also causes a drop in water pressure in the shower.

Dealing with this problem can be really frustrating, and it’s even more likely when you live in a large household. The more people using the bathroom at one time, the more likely you are to get an unpleasant shower surprise. So, what can you do?

How Does Flushing The Toilet Affect The Shower?

This phenomenon usually happens because of your plumbing setup, which is likely a trunk and branch system. This system features a large-diameter pipe, the trunk, that water comes from before flowing to individual locations through separate branches.

Basically, it means your toilet needs to borrow some water from the shower if both are in use at the same time.

Why Does Flushing The Toilet Make The Shower Water Too Hot?

When you’re showering, water is coming from one of the branches of your plumbing system to your shower. You can adjust the water temperature by using your hot and cold taps in the shower to get the perfect temp.

However, as you’re enjoying a blissful shower, a forgetful spouse comes in to do their thing and flushes the toilet. When this happens, you scream, and the toilet now needs water to refill its tank. But, the branch going to the toilet doesn’t have enough water since you’re showering.

Therefore, your toilet needs to pull some of the water it needs from the shower. As the tank refills with cold water, it leaves you with less cold water in the shower. Once the tank finishes filling, the cold water should return, bringing down the temperature.

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Why Does Flushing The Toilet Change the Water Pressure In The Shower?

Besides getting blasted with hot water, another unpleasant side effect of a toilet flush is a drop in water pressure. This happens when your toilet’s tank is refilling following a flush.

Since it’s pulling the water from your shower to refill, you get less water in the shower. Incidentally, this can also happen if someone uses other water sources while you shower. For example, if another family member is washing clothes or running the dishwasher, you could experience a pressure drop.

How Can You Prevent Flushing The Toilet From Affecting Your Shower?

Although a flushing toilet affecting your shower is a relatively common occurrence, that doesn’t make it any more bearable. So, check out these tips for preventing a toilet flush from ruining your shower.

1. Install A Thermostatic Mixing Valve Monitor

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You can install a thermostatic mixing valve monitor to help balance your hot and cold water. This handy device recognizes a drop in cold water and reacts by dropping the hot water, maintaining your current temperature.

Even if the water pressure drops, the monitor will still kick in and make adjustments to maintain your preselected temperature.

2. Adjust The Toilet Supply Valve

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You can help counteract the sudden temperature change and pressure drop by adjusting your toilet valve. This is the supply valve located on the wall behind your toilet.

You would turn the supply valve clockwise slightly to close it just a bit. The result is it will take longer for your toilet tank to fill, but it will help limit the issues you experience in the shower.

3. Install A Load-Balancing Manifold

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Another handy device you could invest in is a load-balancing manifold. This device replaces your trunk and branch system with individual lines for each toilet, shower, washing machine, etc.

The manifold connects directly to your water heater and supplies each fixture with its own dedicated hot-water line. It also connects directly to the main water supply for cold water.

Now, when someone flushes the toilet, your toilet doesn’t need to borrow water from your shower because it has its very own supply. You’ll need a plumber to install the manifold system.

4. Reduce The Amount Of Water In The Toilet Tank

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It’s time for a quick science lesson in displacement. Placing a brick or similar item in your toilet tank can reduce the amount of water needed to fill your tank. This is because the brick takes up space in your tank, so there’s less room for the water to go.

You’ll still experience a temperature change and pressure drop, but it won’t last as long. However, it can also result in a weak flush, which could lead to an eventual overflowing toilet. So, another option to reduce the amount of water is to switch to a low-flow toilet.

5. Remind Your Family Not To Flush

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If you just don’t feel like investing in new plumbing devices or turning valves, or lifting bricks, call a family meeting. If your housemates are forgetful, write up a cute sign, “Please Don’t Flush: Shower in Progress,” and stick it on top of the toilet tank before you hop in the shower.

Or you can make a double-sided sign and hang it above the toilet. When no one is in the shower, flip the sign over so people know they can “Flush Away!”

6. Call A Plumber

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Call a plumber if you’re experiencing dramatic temperature or pressure changes in your shower despite trying these fixes. Even if you had a plumber come out and install a manifold system. If problems persist or return soon after, there could be other underlying issues at play.

A less expensive and time-consuming solution could be switching out the trunk and branch pipe diameters with larger ones. So, call a pro and let them see what is best for you and your plumbing.

Frequently Asked Questions

Why does the toilet back up into the shower?

All of your drain lines from various fixtures flow toward one main sewer line that takes wastewater away from your home to the sewer main. Typically, these lines should be free and clear, so waste goes directly to the main when you flush your toilet.

However, if the mainline gets clogged, it can cause a backup into any of those individual lines. So, when you flush, the wastewater hits an obstruction in the mainline and backs up, likely clogging your toilet. Plus, it also backs up into other nearby lines, like your shower, coming up through the shower drain.

These clogs can result from a number of reasons like tree roots, grease, even kid’s toys stuck in the line.

Why does my shower suddenly turn cold?

Perhaps just as shocking as a burst of hot water is a blast of cold. If your water suddenly turns cold when you’re showering, it likely means someone is using hot water elsewhere in the house.

So, while showering, ask people to limit washing dishes, taking a hot bath, etc. You can also employ some of the fixes mentioned above, like installing a thermostatic mixing valve or a load-balancing manifold.

However, if you notice your shower water just isn’t as hot as you’re used to, or it runs out of hot water quickly, it could be your water heater. The water heater might not be large enough for your needs, or it could require repair or replacement. On average, a water heater lasts for about 10 to 12 years if maintained well.

Toilet Flush Affecting Shower
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