Why Your Water Temps Change When You Flush The Toilet (And How To Prevent it) | WaterWork Plumbing

Common Plumbing Problems, How-To, Water Temperature,

You Flush Your Toilet And Your Water Temperature Changes


Nothing like a relaxing cool shower on a hot day, right? Wrong. Your water temps change when you flush your toilet at the same time. Your 12 year old daughter flushed the toilet downstairs!

The shower temperature was perfect. A shot of scalding hot water comes out of your shower head and your skin is burned. Now your temper is as hot as the boiling water.

The changing water temperatures can be dangerous on your skin—and to your pocket book.

Cold and hot. Hot and cold. Cold. Hot. Freezing cold. Burning hot. What the heck? Thoughts race in your head about the cost of this plumbing repair.



What Causes These Sudden Bursts of Scalding HOT or Freezing Cold Water?


If your shower is running and someone else flushes a toilet, does your shower temperature change? Yes. It happens in some homes.


Why You Get Burned If Your Water Temperature Changes


Your typical plumbing system is a trunk and branch configuration. The wider diameter pipe runs from one end of your home to the other end of your home.

Narrow diameter pipes branch off and provide water to rooms or room fixtures.

If one of your plumbing branches demand water—like a toilet flush—there’s less water available to all other branch channels.

Your toilet uses cold water to fill up. If you flush your toilet, there’s less cold water available to your shower. There’s less cold water to mix with hot water.


Prevent Your Water From Changing Hot & Cold


Fluctuating water temperatures can be a nightmare. The first solution is to have a plan so you can save water throughout your home. Keep an annual plumbing maintenance checklist with a trusted plumbing professional.



Common Solutions To Water Temperature Questions:


 1. Is there a way to avoid changing temperatures by working on the toilet?

The cheapest way to fix the problem is to reduce the water flow amount to the toilet. Reduce toilet water by closing your supply valve a little bit. Your toilet will take longer to fill and might be louder. It reduces temperature fluctuation to other plumbing “branches.”

Solution #2: Purchase a “low flow” toilet. For a quick fix, place a heavy object in your tank. This method will reduce the amount of water available for each flush. Clearing solids from the bowl will be more difficult.

Is it inexpensive to fix this fluctuating temperature problem, or will it require you to replace your water heater?

Maybe not. Check your unit first.


“Upgrading your shower valves might be the best solution. A different water heater will do nothing…A thermostatic mixing valve is the best solution, but note it still takes a brief time for it to adjust to a sudden change in pressure, so a brief cold period will still be noticed.” —BC Workz



 Temps Change; Use Thermostatic Mixing Valves


Look at other options too. Think about increasing the amount of available water within your plumbing system.

A new thermostatic water mixing valve may just do the trick. This installation can reduce and eliminate water temperature fluctuations by balancing the amount of hot and cold water mix.

If your toilet flushes and cold water is reduced, this valve adjusts hot water in your shower. As other fixtures are in use, your shower temperature stays consistent.


“Using up all the water in the hot water tank would lead to a cold shower. And yes, you do have to install a thermostatic mixing valve at each shower and tub. They are used to replace the plain old standard mixing valve.”Tester101


2. Do you have to re-configure your entire piping system?

Yes. Changing to your overall plumbing system will require you to access your budget first.



 Increasing Water Means Increasing Available Water


If you have a ‘trunk and branch’ connection, you’ll need to invest in widening your trunk and branch pipe diameters that flow to other rooms and fixtures, allowing more consistent water temperatures.


Water Distribution With Major Plumbing Renovation


Manifold installation with home runs has a “central load” balancing system. This balancing manifold connects to a dedicated pipe of each fixture of your house.

Installing a different manifold is an expensive solution. Seek professional advice.


Are You Ready For A Plumbing Change?


You can opt for a solid solution that requires an entire revamp of your plumbing system.

Water is about supply and demand:

Water Demand + < Water Supply = Drastic Temp Changes


“The shower temperature changes when you flush (or use water) because the pressure in that supply line has changed. This means less supply to the mixing valve in the same setting. Modern thermostatic mixing valves are designed to keep the total pressure constant. This means that a reduction in cold water pressure (from a flush) is detected and the mixing valve responds by reducing corresponding flow in the hot water. So, the solution to shifting shower temperatures is to install a thermostatic mixing valve.” Matthew PK



Avoid Uncomfortable Showers


Reduce water demand or increase water supply requires some work at the house. Finding the right solution for your home’s plumbing system can take some research and budgeting.



 Do You Have Fluctuating Water Temperatures In Your Home?


There can be several reasons for changing water temperatures. Identify erratic water temperatures in your home and seek professional advice as needed.

Hot and cold extreme water temperatures? Ask a professional plumbing team to access your home today. Contact your WaterWork Plumbing: 248-542-8022