That’s not a failure mode of the firmware. I’m not going to try to diagnose the hardware via the forum, especially where you’ve taken a heat gun to it. There are a couple things you can do:
You can try to reflash the ESP8266. I gave instructions for that in this post IotaWatt solid red light - won't start - #4 by overeasy
The other thing you can do, if you are in the USA, is send it to me and I’ll take a look at it. If you decide to go that route, PM me and I’ll give you a shipping address.