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Shower Gets Hot When Toilet is Flushed: Fixing A Temperature Change

The sudden eruption of scalding hot water in the shower is a frightening situation. The last thing someone wants when they are in the shower is lava-like water suddenly piercing his or her skin. Not only does this outburst of hot water cause severe pain and inconvenience, but it also leaves the individual with severely burned skin. Talk about starting your day on the wrong note….

The most obvious question to ask when sudden hot water from the shower spears your skin is “Why does this happen?” The answer to this question is actually more simple than you might expect.

Most homes run off of a plumbing configuration called a trunk and branch system. This is when one large diameter pipe runs the course of the building, with smaller pipes branching off the larger pipe. So, when one of the smaller pipes requires a significant amount of water (i.e. flushing the toilet), the supply of cold water depletes from the other smaller branch pipes. Thus, less cold water mixes with the hot water in the other branch pipes, increasing the temperature exponentially.

Trunk And Branch Plumbing System


Fortunately for everyone who suffers from the sudden rush of hot water when showering, there is a fairly simple and cost effective ways to eliminate temperature fluctuations in showers all together.

Install a Pressure Balance Valve (Mixing Valve)

The most cost effective method to eliminating temperature fluctuation in the shower is installing a pressure balance valve. This device attempts to stabilize temperature in the shower, despite sudden changes in hot or cold water supply lines (i.e. when the toilet flushes). Older homes tend to not have a pressure balance valve installed since the valves weren’t mandated in houses until recently.

Unfortunately for homeowners who don’t have a pressure balance valve installed, the valve isn’t universal. Furthermore, figuring out which size pressure valve fits in your piping system is difficult. You have to take into account whether a balance spool or diaphragm style of valve is more ideal in your piping system. You have to figure out whether a cycling or non-cycling valve works best in your home. And lastly, you have to determine the appropriate flow rate needed in your home.

This can sound overwhelming and complex, but fear not because Terry’s Plumbing has numerous years experience in installing pressure balance valves. You’ll be on your way to steady water temperature in no time at all.

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