We have a small mountain cabin that is used on weekends with an LP furnace manufactured by Nordyne probably 90k BTU. It is vented through the wall via PVC.

A few years ago the furnace wouldn't fire and I believe the control board was replaced for $800. This winter the tank ran empty and was recently filled. The furnace fired right up, there didn't appear to be air in the line needing to be bled. The unit continued to work well for the next few days while we were there.

Returned 2 days ago and I noted that the tank was still 80% full. O.K. but I thought that odd since it has been very cold. Heat fired right up and warmed the cabin. Later that evening I noticed that the temp had fallen to 65 despite thermostat at 69. I unplugged the power to the furnace allowing the electronics to reset and it fired right up.

This morning I awoke to 54 degrees. I had to again unplug the controlled to get it to fire. Now I am concerned that when we leave the heat won't work and the pipes will freeze.

Any idea as to what is causing this and what a ballpark amount would be to repair?