Why Does The Shower Get Hot When The Toilet Is Flushed?

Were you burned the last time someone flushed the toilet while you were showering? It's a simple plumbing fix.

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Hey Brainstuff… have you ever been taking a shower… y’know, gently scrubbing your body… maybe singing Boston’s “More Than A Feeling…” when all of a sudden the water becomes scalding hot, potentially burning Your Special Downstairs Area?

I’m Jonathan Strickland and I’m here to tell you that it’s not just you.

Before I teach you how to fix your plumbing so your shower no longer scorches your flesh, please allow me to first explain how the modern “commode” works.

A common configuration of pipes in homes is what’s called a “trunk and branch” system. It’s like a tree with one large pipe (y’know, the trunk) that has several smaller pipes branching off to things like your sink, laundry machine, shower or toilet.

If one of this pipe-tree’s “branches” needs water -- like when you flush your toilet -- there’s less water available for the other branches on the tree.

There are around 3 gallons of water in that tank on the back of your toilet. So when you pull the handle, it flushes all that water to send whatever you’ve disposed of down the sewer pipe. The tank subsequently refills, taking water away from the other branches.

And here’s the important part: your toilet only uses cold water.

So the reason your shower gets hot is because the flushed toilet takes away the cold water that was available in the system to mix together with the hot water coming out of your shower head.

And it’s not just your toilet that can contribute to this problem. Any appliance using cold water can steal it from the shower: washing machines, sprinklers, even bidets.

There are several ways to fix this water temperature problem and I’m going to present you with a few, but if you’ve got other suggestions, please let us know in the comments.

The simplest method is to adjust the valve under the toilet’s tank. Most of the time these can be tightened so the toilet takes longer to fill. Unless you're the kind of person who is constantly discharging bodily waste, you probably don’t need the tank to be primed immediately. This will take less cold water away from the shower.

A similar simple solution is to place an object -- like a brick or I don’t know… a human skull -- inside the tank so it doesn’t use 3 gallons every time you flush.

There are more complex plumbing fixes available as well: like increasing your trunk pipe’s diameter, installing a new mixing valve, or renovating the whole system. But all those are gonna cost you cash money… and let’s face it, if you wanted to spend that you wouldn’t be watching an online video for home repair answers…

SOURCES:

http://www.inman.com/2007/06/06/dont-flush-toilet-im-showering/ (tester 101)

http://priceonomics.com/post/45684980159/why-does-the-shower-water-get-hot-when-you-flush-the

http://misterfixit.com/whoflush.htm

https://www.itsdone.com/cause-of-water-temperature-changing-after-flush/