Immersion with Otter Dualstat Thermostat

[John Carroll]

I have a 52 year old Santon dual element immersion which has the sink/bath change over switch together with a Otter dualstat thermostat mounted on top of the immersion, (3 wire) I installed this in 1972 (new house, then) and I self installed a modest solar thermal system 11 years ago and installed a new twin coil cylinder, I removed the immersion from the old cylinder and reinstalled it in this cylinder. Its still working perfectly but I only occasionally use the sink (short) element).

It doesn't have the rod type thermostat so it would seem that these Otter type stats are just surface mounted to the immersion top. Below is a photo of mine and I also include a photo of a immersion from someone who had a Otter Dualstat K71 stat, can't remember if mine is K71 but I imagine the operating principles are the same.

Someone may have renewed one of these in the distant past and know how they work?

Edited May 18 by John Carroll