user69781: I have a 2 wire thermostat. R is +24VAC, W is Heater. I have no Ground wire (C), and I cannot open the thermostat.
When the heater goes on, the thermostat internal relay gets powered and connects R and W together.
How can I detect when the heater is on from those two wires?



user45534: With checking the temperature in the room. When the contact is closed store the current temperature. Check after a minute the temperature again. If it is higher, the heater is on.

69781: <p>I have a 2 wire thermostat. R is +24VAC, W is Heater. I have no Ground wire (C), and I cannot open the thermostat.</p>
<p>When the heater goes on, the thermostat internal relay gets powered and connects R and W together.</p>
<p>How can I detect when the heater is on from those two wires?</p>
<p><a href="https://i.stack.imgur.com/aHrjL.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aHrjL.gif" alt="Thermostat" /></a></p>
<p><a href="https://i.stack.imgur.com/FKmln.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/FKmln.png" alt="circuit" /></a></p>
 45534: <p>With checking the temperature in the room. When the contact is closed store the current temperature. Check after a minute the temperature again. If it is higher, the heater is on.</p>
