I got a used Lopi Spirit and everything works great except that the flame adjustment valve doesn't seem to change whether it's on low or high. It's always on full. Is this a valve issue or am I dealing with a thermopile issue or something else? It's a manual valve knob and turns as it should so I can't imagine there's mulch to go wrong there. I just don't know if it's something that could be controlled by electronics in this model.