hot shower

Everytime a toilet is flushed or a sink is used while the shower is on that person gets hot water only! ouch! Please advise to the cause.

The shower controls are old. Newer models have ways to determine the difference in hot and cold water and adjust it accoringly. There are no electronics involved, just special valves.

So you dont think its because bad venting ? what is the test for
bad venting anyway is it turning on shower , sink and flushing toilet at the
same time and if there is suction of some king on the shower or sink its
the venting system

Could be low water pressure.

Bad ventind or lack of a vent would cause the water to drain slower. The vent only involves the drain line. This would not affect the high pressure line. I’d bet my life that its the mixing valve.

If older house it could be the galvanized pipes or a mix of copper & galvanized pipes… The pipes corrode from the inside-out.

On a well, could be a buildup of minerals inside the pipes & mixing valves.

Old mixing valves can even have chipped valve seats & chipped washers that reduce water flow.

Low water pressure: Bad pipes, Bad Valves, Bad Mixers, Well situations

Poor venting: Sink and tub drain slow, toilet does not flush with one flush

These are just possible indicators. Other situations could be the cause also. eg: hair clogs, etc.

A preasure ballanced valve would help with this situation. The valve adjusts itsself when a fluctuation is temp occures. You may feel a reduction in water preasure but not the hot/cold difference.

Without one it’s a good way to tell the kids to get out of the hour long shower. Just flush the toilet a few times.

Are there both a hot and cold control valve to operate the shower?

Or just one valve?