also I wanted a control for a bathroom extractor fan to run when the power shower was used , but not attached to the light switch by using a sensor attached to to the shower hot supply
Cool projects, actually. My bathroom situation is/was:
An IR heatlamp and a slow turn on green spotlamp and fan in one housing. These are controlled by a mechanical timer (20 minutes) and a delay on break for the shower. So, you have light/fan as switches and IR on a mechanical timer. The extraction fan runs on a delay on break. The timer is in the attic and has to be replaced, but it's been at least 40 years.
I've thought about a flow switch to turn on the extractor. The bathroom fan also needs a decent check valve.
Normal lighting is a photo activated LED night light.
Then there is "over the mirror" globe lighting. One, two or 3 globes on. Nearly 99% of the time the night light is all you need.
The more I think about it, the convenience of actual temperature control would be really nice.
I wish I would have put in the dual valve version of the shower control rather than the spout diverter and On/OFF. The dual valve gives you one for the shower and one for the tub. That's more convenient for those taking a shower sitting on a shower chair.
I also forgot to make the shower have a 45 degree bend rather than a 90 degree bend.
Issues (breaks) happen when one rests their feet on the tub spout if plastic. The "diverter" right now "stays up" and this is better when using a chair in a shower.
I plan on adding a recirculator too at some point too.