Can I replace a 2-wire line thermostat with a 4 wire?
Cumberland County Pennsylvania home energy
Tell me more about your old thermostat. You called it a line thermostat. Is it a low voltage thermostat or does it work with line voltage, 120 V or 240 V? Line voltage thermostats have standard home wiring going to them, at least 14 gauge. Low voltage thermostats have very small wires, 18 to 22 gauge.
Four wire thermostats are usually low voltage. Your new thermostat will need to match the voltage on the old one.
Most thermostats have letter codes on each terminal or screw hold the wire. The letters will need to match. Wires will go to the same lettered screw on the new thermostat as the old one. If the codes don't match the new thermostat should include instruction sheet for conversion from one code to another.
There are some YouTube Videos to help.
To start see https://www.youtube.com/watch?v=HDWV5zJokPA
This video has a 2 wire thermostat.
Thanks for your answer. I had failed to mention that it was a four-wire, line voltage thermostat and wondered whether I could put the two breaks in parallel. But one break was merely a switch so I just didn't use those two wires. I added a neon light across the stat so I can see whether the contacts are open or closed. It's not ideal since the light is on when the heater is off. But I know what it means and nobody else cares.
It should work if you can identify the same connections on both thermostats.