Why does the shower get cold when a toilet is flushed?

Question

If it were using the cold water, why wouldn't the water get warmer?

My showers always seem to get hot, but I know the toilets aren't hooked up to the hot water... Why is this?

Answer 1

When the toilet is flushed, the toilet is "robbing" pressure from the shower, which is usually close to the toilet. As the COLD water pressure goes down from the toilet flush, the HOT water pressure is higher, therefore the water gets hotter as the COLD pressure goes down. There are several shower valves on the market that compensate for this problem. Unfortunately, it requires a total removal of the old valve and installation of the new one. These new valves are single handle valves. Delta makes one that is called the "Monitor" or "Scald Guard". These faucets automatically adjust the pressure. When the toilet is flushed, the person in the shower will never be able to tell!!! Hope this helps! Good luck!!

Answer 2

I've always had the shower get hot when the toilet is flushed. The toilet uses a lot of cold water to flush, preventing it from getting to the shower. If you shower goes cold when the toilet is flushed, then it might be using the hot water.

Answer 3

You have low water pressure going to the shower on the hot water side. Probably scaled pipes. When the toilet is flushed (cold water), the cold inlet to the water heater loses pressure also, thereby reducing the pressure on the hot water outlet of the heater. The scale does not build up in the cold water pipes as quickly as it does in the hot water pipes, so you have better flow on the cold side of the shower. I suspect the house is old enough to have galvanized iron plumbing, or a dielectric union was not installed with the water heater.

Answer 4

The problem is a drop in pressure,can be fixed by going to a hard ware store than install a equalizer value,as water is flushed the value balances the difference keeping both happy,water warm where needed and waste ,well you the rest.Value is installed at the shower point.

Answer 5

If you are using an oilburner with a domestic coil, the coil may be partialy plugged with scale. The overall water pressure drop may be just enough to stop the hot water and not the cold. I suppose that would also be the case with an Instahot type heater though I've never worked on one of those.

Answer 6

Your hot water heater works on pressure of cold water pushing the hot water out of the tank. When you flush the toilet, the pressure that was pushing out the hot water is interrupted, causing a loss of hot water pressure.

Answer 7

Newer shower come with a built in pump to prevent this problem while the older model like your need a certain line pressure to activate the hot water switch and will switch off when there is a drop in line pressure and switch on when there is a min pressure requirement.From what you have encounter most probably the water pressure in your area is not adequate.Get in touch with the ultility technical people to boost up the pressure in your area

Answer 8

the water main or line force pressure both side cold direct to the sink, toilet ( reminder is the shut off value fully open ? is it low flow tank 1.5 liter. whats the size of the pipe in the house ? when you flush the force or pressure pushing the water both hot and cold how's the water heater inlet side is it fully open to get the maxium pressure from the cold water ?, if not their is no force pushing the water for the hot.

Answer 9

in our house the shower pressure lessens a bit and the water gets hot when the toilet is flushed, teeth brushed, or hands washed. god forbid someone turns on the hose outside!

Answer 10

you know why!
the cold water is being used in toilet too at the same time which reduces the cold water flow to shower...