How can I test if a Cotherm TSE or TSR plug in type immersion thermostat is working or not?

Wayne Harrhy • October 15, 2025

How can I test if an immersion rod thermostat is working or not?

QUESTION


  • How can I test if Cotherm TSE or TSR plug in type thermostat is working ?
  • Do I need to remove the whole element ??
  • Do I need any special knowledge or equipment ???

ANSWER


DO NOT EVEN BEGIN ANY OF WHAT IS CONTAINED IN THIS BLOG UNLESS YOU ARE SUFFICIENTLY     QUALIFIED OR COMPETENT.


Once it has been established there is the required power to the thermostat and it isn’t as simple as a breaker re-set or a fuse change, here are a few initial rudimental tests to carry out


  • You may find it easier to remove the thermostat for testing

- Although the thermostat may seem fixed to the element it is removeable separately


 - The thermostat is located on the element via two spade connectors


 - The units are designed to have a really tight fit, so it may need some force
  • Look for any signs of damage

- Are there any burn or scorch marks anywhere


- Has the “over temp safety” activated 


- The over temp safety is a resettable feature


- Simply take a non metallic probe & push gently until you feel a click


- If the safety has activated, there will be no current flow when undertaking the tests below
  • Once the visual checks are completed, with no sign of failure, we can undertake the electrical test

- We are going to undertake a continuity test, for more information see

  https://www.youtube.com/shorts/wNx73o-3ESw


- The thermostat is a temperature activated switch


- You will need to test that the unit is both making and breaking contact


- The TSE & TSR thermostats are single pole on the regulation  

 

- Set your electrical tester to continuity with one probe on terminal A 


- The second probe on the LIVE spade connector


- Now  turn the temperature dial from 1 to 5 and back again


- Your tester will buzz when contacts are made and be silent when they are broken


*BE AWARE IF THE AIR TEMPERATURE IS LOW, THE ROD SECTION MAY NEED TO BE WARMED*
Why are the Cotherm TSE & TSR thermostat terminals marked A & B?

Why are the Cotherm TSE & TSR thermostat terminals marked A & B?

By Wayne Harrhy • August 20, 2025
On a Cotherm thermostat, the terminals are marked A and B to denote the electrical live input and output, respectively, for a simple switch circuit. Specifically, A is the Live (Brown) connection that receives power, and B is the Neutral (Blue) connection that the thermostat switches.