You need a proportional temperature controller you need to look up on line as there are many suppliers. As you set temp a thermocouple measures temp and switched power as necessary.

David

Hi Fizzy

I agree the thermostats fitted to immersion heaters may be a bit coarse for some applications but they do seem to be consistent in switching temperature.

For finer control you will need to fit an electronic probe and control that will switch the element on for short periods until the set temperature is attained. Positioning the probe is important but it is unlikely to achieve all water at the same temperature if you don't have positive means of circulating it in the tank.

By whichever electrical method used for heating the water temperature will be controlled by a thermostat or similar device, even your variable speed control unit.

Emgee

Edited By Emgee on 16/07/2018 21:32:17

Edited By Emgee on 16/07/2018 21:33:28

John, I had already suggested a method of control, almost the same as your suggestion but I did add a circulator would be required to ensure even water temperature in the tank.

To use a motor speed controller is a no go as suggested by my reply, but it would heat the water by switching the supply on, just add a stat as 2 wire on/off control cct.

Emgee