Ben K Redwood City , CA May 30, 2015 Appliance: Thermador PRG304US Thermador Prg304us: Front left burner would not emit gas in any knob position ignitor worked properly. How to replace Nut. The root cause of the problem was a bad potentiometer. The carbon tracks were worn out, and not providing electrical contact that energizes the gas control solenoid. In order to test the solenoid, I had to disassemble the cooktop, and the nut and "jet holder" were welded together from years of exposure to heat. Disassembling the old parts was difficult, but installing the new ones was easy. Note that the new potentiometer (AP3782975) appears to be a direct replacement for the old one (AP2825521). Thermador PRG304US 4 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 15-30 minutes