Laars Lite LLD325P

[jjrepko]

I've fixed and replaced many parts in this old heater from the Teledyne era of Laars. New problem: it runs for a minute or two,
then the flame turns off for 2-3 min., then relights and continues that cycle all day long. I dialed down the pressure valve - no effect. So I'm thinking it may be the thermostat but I don't know where that is located. Does anyone know? Or have any other ideas as to the cause?

 

[sktn77a]

If I remember correctly, the temperature sensor is located in the inlet manifold. The entire replacement kit is quite expensive ($100-$150) - includes the thermostat setting plate and on/off switch on the front of the heater.