Fishing for specialty t-stat

[herding_cats]

First time I ever heard of a hydronically heated towel rack. Usually, they are electric with an integral thermostat. As to your dilemma, there are plenty of industrial controllers with sensing probes that can go in your wells. Problem is the controllers probably won't lend themselves to your decor. Maybe there are some that are blue tooth, WiFi or ethernet enabled so that you can control them from your phone?

-Hal

Years ago I watched a plumber pipe in the hot water in and out of the wall to custom build the heated towel bars. 3/4 copper towel bars with the water from the shower incoming heats it for you as you are in the shower. Pretty clever.