Thermador left front simmer burner - lots of posts on this troublesome item.

I replaced the control box and both potentiometers ($180), which got the left front burner to start working again. But that did not also fix a years old problem where the burner works when stove is cold but NOT when stove is hot. Appears to be the gas solenoid because it 'clunks' and let's gas flow when cold but not when warm.

Is that a reasonable diagnosis and is the solenoid easy to replace? Looks like the solenoid passes through to the bottom side of the burner area (between the burners and the stove ceiling). Would love to fix this thing once and for all!

Thanks to Gene and others for helping the do it yourselfer.

This forum is pretty dead. Some good advice but not very active with experts.

If anyone has the same problem with simmer burners working when cold and not hot, it was the solenoid in my case. Thee is a clunk sound when the solenoid fires. If you hear that in one simmer burner and not the other, it's either not sending power to the solenoid (logic board) or the solenoid is flakey. And, they can be removed from the same place as all other burner work is done....under the cooktop. I had thought the solenoid a might be a problem, as they are deep and run underneath the sheet metal of the burner area. Turns out that once you remove the bracket, it pulls up and out for service.

TURN OFF THE POWER, when replacing a solenoid. I was testing for voltage to the solenoid when it slipped slightly and the hot lead made contact with the sheet metal. Bye bye burner logic board. Fried at least three components (two resistors and a triac? Or transistor?). That's a $177 part. Be careful.