Continue the penetrant bath. Easy taps on the shaft. Check if the valve is open. If it is, the exhaust will have a path to exit. I would not suggest using the 'torch' method, a heat gun and or a 1500 watt hair dryer will apply needed heat.....and keep soaking it as you heat it/ tap it. Good luck with your project.
Note: the original thread for the temp in the head is 3/8 NPT. If you need to repair the opening, make sure you have the space for the themo tube to insert.
