Furnace Is Either Too Hot Or Too Cold... - HVAC - DIY Chatroom Home Improvement Forum

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Old 01-26-2011, 08:35 PM   #1
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furnace is either too hot or too cold...

I have an 8 year old gas furnace. A few weeks ago it started turning off and on every three minutes or so. When it was off there was no power at the thermostat...which is wired to the furnace, not battery.

So, I called my HVAC guy. He came out said I had a dirty filter (it was only 2 months old but was dirtier than normal.) Once he pulled the filter out it ran fine.

Three days later it started happening again (with a clean filter). He came back. He did some cleaning inside and lowered the gas pressure to prevent the overheating. All seemed fine for a few days.

Then it happened again. This time, I immediately took out my high-allergen filter I normally use and put in a cheap one that barely filters. The furnace runs....and runs....and runs....and runs.... it gets up to temperature but never shuts off....It never goes above temp either, though. I verified it's not just the blower running, it is heating the entire time.

HVAC guy came back out and cleaned the AC coil that he suspected was blocking the airflow. Turned out it was not that dirty at all, but at least it's been ruled out... he lowered the gas pressure again to prevent it overheating. Again, all seemed fine and he left.

Since he left, the furnace has been running non-stop but can't get the tempurature up above 65, even though it's set for 70 (and it's not that cold outside). There is barely any air coming out of the vents...literally none in the farthest room. I pulled the high-allergen filter out, put the cheapo in. The air is blowing fine now, but still not heating my home.

I don't want to keep throwing money at this and would like to solve the problem. I got my gas bill today and about fell over. Between December and January I used more gas than I normally do in an entire winter! Nothing has changed in my home that should be effecting gas usage to that degree.

Any suggestions? The furnace is hogging gas and when the gas pressure is up it overheats constantly, but when it's down it's not hot enough to heat my home...


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Old 01-26-2011, 09:27 PM   #2
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Sounds like an air flow issue. Lowering the gas pressure keeps it from overheating but it also lowers the BTU output and the efficiency. Those ultra allergy filters are hard on blower motors. No way to tell without being there but I would lean towards a new blower motor, assuming the capacitor is good.


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Old 01-26-2011, 10:02 PM   #3
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He did verify the capacitator was not cracked. The blower is working, but it may not be at full capacity. I'll put that next of the list to check.

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Old 01-27-2011, 03:49 AM   #4
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Get a different tech. He now has your gas lowered too much, so your furnace could be running in a manor that is harmfull to it. And cause you to have to replace it down the road.

The insulation in the blower compartment may be coming loose and pulled in toward the blower, choking off some of your air flow.
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