Furnace only works when filter is removed

14 Replies

A tenant informed me the property will not heat above 58 degrees.  The furnace is on but nothing is happening.  Initially we thought it was the thermostat but that checked out.  The filter was dirty but not horrible.  Upon removing the filter the furnace started operating properly.  Putting a new filter in did not fix it either.  Not sure if it has to do with the air flow, type of filter, etc.  Has anyone encountered this?  I have a professional coming to look at it but want to compare that with what I may hear from you.

It makes no sense. Unless there is some sort of air flow sensor. No air flow, no worky.

It could be that the fan is so dirty that air flow is already restricted and when the filter is in the air is not moving

Could there be a low suction pressure switch or a differential pressure switch across the filter? If so perhaps there's a malfunction. I wouldn't have a clue as to why there would be such instrumentation in a residential application.

I'd like to hear the resolution!

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I have had this happen three times at my personal house. The first time we placed a service call and the technician said it was from the particular filter we had in the unit. We had used a pretty high filter and he said that the higher they are the worse they can be for the furnace and air flow. We started using lower filters and it worked fine, but when trying to pick out the filters later on, since they vary by place purchased (i.e. Lowes, Home Depot, Walmart) we ended up with the same issue two more times. The last time was just this past weekend and we went with a Rhem FPR 4 from Home Depot and it has worked fine ever since. Seems odd that the companies make filters that work TOO GOOD for a furnace...

Thanks for the responses so far.  It is a gas furnace.  Its looking more and more like I should just put a wire mesh screen as a filter since buying what is supposed to be "good" (reduces allergens, dust, etc) just causes more harm.

I'm not too familiar with furnaces but I had a similar issue with a heat-pump system. 

Everything seemed to be working except the air handler would not cycle and blow air. 

"VERY CAREFULLY" you can try spinning the fan motor with your hand to start it up. This requires taking the cover off your unit if you know how to do that. You have to spin it in the correct direction so try both ways if you are unsure. If the fan motor starts spinning, then it is a bad capacitor. 

The capacitor stores energy and helps supply enough power when the fan is called to engage. With the filter in, there may not be enough power for the fan to start, where as with the filter removed it doesnt require as much energy and it is starting. 

An indication of a failed capacitor is it will be bulged out on the sides. They are around $20 for a new one. The Capacitor is normally right near the fan motor and wires will run from it to the motor. 

Here is an example. The little square box with wires is the Cap. 

*As with any electrical repair, make sure you cut power at the panel before replacing the capactor. 

Arlen is probably the closest to correct. You have air flow issues. I am an HVAC tech. You need pull the blower out and clean the assembly. The key is putting it back correctly. If that doesn't do it you may have gas pressure issues. If you don't know what your doing there, you better call a tech. $100 well spent and safe. If the fan is not coming up to full speed it could just be a $20 capacitor.

I had the same issue on one recently. The filter was very high density (you couldn't see any light through it). It looked like cloth. We put one of the rinse-able mesh filters in and that was that. 

FYI, the tech discerned this while I was standing there. There was nothing else wrong with the unit.

As a side note: I only use the cheaper filters in my furnaces. I have 3 HVAC experts in the family and they each have told me that the "premium" or "allergen" filters are hard on the furnace and will reduce its life.

Resolution Update

My tech informed me they found the owners manual to the furnace sucked up into the blower compartment causing the airflow problems.  Who would have thought?!?!

Thanks for the responses.  From what I learned I think I am going cheap filters all the way to not strain the fan.  Amazon seemed to have the best prices....under $20 for 12 filters...not too bad.

funny. Glad it was a simple fix. Had a similiar problem with AC not cooling.

My tenant had replaced the filter, which was due for a change, a cheapie brand. The fix was to flip the filter around...so the little arrows align with the air flow.

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