I Have a customer with a Cozy brand direct vent space heater that will only work for about 2 weeks until the thermopile has to be replaced. I believe the gas control is bad but have not been able to prove it as of yet. Both times I have went back the pilot will not stay lit, yet the old thermopile was still genetrating 300 to 450 milivolts. I replace the thermopile with a new one which generates 800 milivolts when new and the heater works fine. I believe the gas control is faulty but want to prove it before spending 150.00 on a new control. I also know this unit has had problems in the past before I worked on it, but I am unable to find out what has been done in the past as there was a different person living at the place then. Does anyone have any suggestions? I believe the control is a robert shaw it has no info on it to tell for sure. I have removed the thermostat from the circut an tested the operation and it does not seem to matter, when the main valve is energized my milivolt signal drops to between 230 and 250 milivolts and when I open the main valve knob and allow the burner to light the pilot signal goes up to around 330 milivolts.