My gas furnace ignites normally, blower starts, runs for 1 minute, then blower shuts down, but flame stays lit. about 1 minute later blower starts again, runs for 1 minute than stops. Flame is still on. Furnace hasn't achieved desired temp yet. This is my old house furnace[forced air propane 1991 80% +] I installed recently in my double garage in north Dakota[cold]. I have brought garage temp to 60 degrees with a secondary heat source to rule out too cold air over heat exchanger. It ran normally in house but I cant get it to run right in garage.