Some time ago I found my furnace (gas, forced air, downdraft) was getting stuck on, blowing cold air. I could reset it, but it would happen again after a while.
After calling out a service man, I was informed that the high limit switch was tripping. The furnace had been using a very light-weight filter. With a heavier duty filter, it overheated easily. With extra air-flow (bypassing the filter) it never overheated.
We opened more exit vents and even added an intake directly to the return passage of the furnace. This seems rather a drastic hack, and I still can't use standard paper filters, for example. Any ideas?
Update: Furnace is ~15 years; I had a service man to check high limit switch etc.
Best Answer
It's common for HVAC systems to be improperly designed. It's also a common misconception that it's okay to close vents. If a regular density filter is restricting airflow (and causing the unit to heat up too much and trip a safety switch) then you need to do something about the airflow.
In general it's not a good idea to close vents because it changes the "static pressure". I don't know the details but basically you don't want the pressure in your vents to be much higher than the pressure in your house. If so the fan is working too hard and there isn't enough air passing over the heat exchanger.