[Lack of HP]

Well it is 90 degrees, both ac's are on and the furnace is on. Will not shut off unless you turn off propane tank. Had this happen about 3 weeks ago. Took it to CW and they replaced two boards. One in furnace and one in back AC so they said. Two days later same thing. Called mobile service repair out, paid out of my pocket said it was my thermostat. Replaced it. Worked fine for about 10 days. Left that location and while in travel furnace started coming on by its self. Stat completely shut off. Shut down twice by shutting off propane but will not stay off. Has anyone experienced this or ideas. Thanks Joe