Has anybody made a temperature controller for a Thermar electric hot water demand heater? Or have any suggestions? The Thermar company was bought out many years ago and the products discontinued. The Thermar is a tankless 220VAC in-line hot water heater that operates only when you open the hot water tap. The control circuitry has died on it. It used a special IC no longer available.
When the Thermar worked it was very good and I have 2 of them, with burned out controllers. Temperature was monitored by a thermistor and the heating element was controlled a triac (which kept burning out). I replaced the triac with a SSR. The Thermar uses a reed switch & magnet to detect when the water turns on.
Most of the heater works, except the controller. I can heat the water manually by operating a push button switch to turn the heating element on and off via the SSR and a small 6V battery. For my wife to have a shower I press the button approximately 2 seconds on, 2 seconds off while listening to the water begin to "sizzle" and press less often to avoid getting it too hot - which pops the thermal cutout. I use a wood stove to heat the water in winter.
I propose to monitor the thermistor input and control the heating element by the SSR. I could use the output from the reed switch as a go/no go logic switch. Has anyone tried something similar? This seems like something the Arduino should be able to handle quite well. A good project.
I don't need to know what temperature the water is beyond too cold, too hot.