In the past, if someone was showering and the toilet was flushed. The water in the shower would go suddenly hot or suddenly cold.
Why did that happen? What changed to prevent it?
In: 111
The water lines in your house are under pressure. When you’re having a shower let’s say you mix 50% hot water line and 50% cold water line to get the right temperature. When you flush the toilet, the cold water line is opened inside the toilet to refill the tank. This drops the pressure inside the cold water line, so at your shower valve, it reduces the water input in the mix. So now you’re getting something like 60% hot water to 40% cold water. So it comes out much hotter. As a safety measure, people would sometimes hook up your toilet to the hot water line instead, so you the water would turn cold instead of scalding. Still unpleasant but at least no injury.
New valves use a thermostatic pressure balancing system. It wants to stay the same temperature. So when the cold water input drops, it keeps the ratio of pressure consistent and drops the hot water input as well. So you keep your 50/50 hot/cold mix. These valves restrict the overall water use more than the old ones did, which means that the water flow doesn’t noticeable change much when someone flushes.
Shared water lines where when the toilet needs more water (to fill its tank up) then less cold water gets sent to the shower.
In the US, it became part of plumbing code to add in values to fix this.
https://www.howtolookatahouse.com/Blog/Entries/2019/12/when-were-shower-control-valves-first-required-by-code-to-be-pressure-balanced-and-temperature-limiting-single-handle.html
_____
EDIT: As the other user mentioned, you could hook up the hot water line to the toilet which would cause the shower to get cold when flushed. I would assume a washing machine and dishwasher, if also sharing the water line, also could cause this.
Many people just turn the toilet fill valves to be partially closed to prevent this. Then the cold water pressure diverted to the toilet is much less. Most toilets primarily use the toilet tank water for flushing and work fine with less input water pressure they just fill up the tank slower after a flush.
In older construction what would have changed is the city improved it’s feed or water pressure. It’s not dead lots of places still have the problem.
Latest Answers