Reddy heater R55tb

What is pictured is a propane heater. two problem areas come to mind. one) the hi limit cutout, and two) the flame sensor. the hi limit is a normally closed device that is bolted to the back plate of the fire chamber. its two wires go to the cappilary of the flame sensor. the flame sensor is of the j-k thermocouple. it generates a millivolt signal to keep the pilot valve open. the flame sensor generates a dc output to the tiny electromagnet inside the main valve. when you start the unit, a hot surface igniter heats up, the main valve opens, a signal is generated to keep the valve open. if it doesn't sense a flame it shuts down and goes into lockout. change the flame sense unit first. what you can also do is temporarily put a jumper wire on the two terminals on the cappillary of the flame sensor.