when you’re showering and the water suddenly turns icy cold or scalding hot for a few seconds before returning to its previous temperature, what’s happening?
In: Engineering
Somebody opens a tap somewhere else. The water prefers the other way if pressure loss is smaller that way. Therefore, no hot or cold water arrives at your tap anymore.
Water temperature in the shower is determined by the mixing of cold water + hot water from the two different pipes in your house.
If the water pressure suddenly changes, like for say someone flushes the toilet, the cold water pressure in the shower drops and the temperature increases.
Most showers these days have valves designed to minimize this effect. Because suddenly having nothing but scalding water can be dangerous.
The valve mechanically senses the drop in pressure and adjusts the pressure of the other pipe to compensate, but there’s still a fluctuation in pressure and temperature change. It just isn’t as bad as without the valve.
Your valve might also be worn out.
Water is only heated at a set temperature.
Cold water is mixed with that one temperature.
Sometimes the water isn’t constant, so it hiccups, usually just a pressure drop or increase from the water main, through the valve changing the temperature for a second.
What’s weird about reading this is that it made me realize this happens in my flat, for a couple weeks around this time of year (spring). But, that’s the only time. Every year. Building is only 20 yrs old.
The water coming out of the shower head is a hot and cold stream mixed together inside of a valve.
The valve balances the pressure between the two streams by opening the hot stream and closing the cold stream as your turn the valve towards from cold to hot.
At any given temperature coming out of the shower head, the hot and cold streams’ pressures are balanced to give you that temperature.
If someone starts the washing machine on a cold cycle, the washing machine is letting a bunch of cold water in. The pressure of the cold water lines in your house drops. If you are in the shower, the lower pressure cold water would allow more hot water to push in through the valve, causing the shower water to get hotter.
I have an on demand water heater not a hot water tank. It is fairly common to experience the “cold water sandwich” with those as well for a variety of reasons; low water pressure as everyone else stated, bad mixing valve, scale build up on hot water pipes, bad crossover lines, clogged filters.
For an example take two pipes, one supplying hot water and the other, cold water.
A **shower** gets water from both of these pipes and depending upon the adjustable valve , we get our perfect bath mix at desired pressure.
Imagine a **tap** which gets water only from the cold pipe.
While taking a shower, if someone else opens the tap, the water from the cold pipe prefers the tap instead of shower since the pressure loss is lower that way. Hence, the shower gets hotter. The person in the shower will have to re-adjust the valve towards the colder side, so as to allow more cold water from the pipe to reach the shower valve.
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