Furnace blower runs but no heat


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Old 11-23-18, 04:47 AM
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Furnace blower runs but no heat

Amana DMS90904CXA -Installed 2004 in 2,000 sq ft ranch in Michigan. Has Ecobee thermostat that has worked fine for about a year. Shortly after heating season began this fall we wake up to no heat. The blower runs but no heat. Had It serviced by a HVAC tech who cleaned the igniter, replaced filter etc. it worked fine for about a month before waking up to no heat again. A different Tech came out & checked the igniter then put it back in and it fired up fine. Nothing was changed. He rechecked various controls but couldn’t find anything wrong. It worked ok for a couple weeks and then no heat again. Different tech came out and I reviewed this history with him before he touched anything because It seems that the minor tinkering with the controls only temporarily fixes the problem. Then they can’t find what really is wrong.
I shut off power for a minute and restart. While the blower and inducer motor is running I went outside and put my hand over the exhaust pipe. Then the burners fired and it worked fine for several hours. But now it’s out again. I ran a plumbing snake down the exhaust pipe to make sure it’s clear. I put my hand over the pipe for a moment and it fired up again and is running now. Also, earlier I noticed a LED light that blinked a couple times then stopped.

Moderator note: two threads merged



 

Last edited by PJmax; 11-23-18 at 08:52 PM.
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Old 11-23-18, 05:13 AM
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Blower runs but no heat.

What error does the unit fail on when you have no heat?
 
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Old 11-23-18, 06:21 AM
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I apologize for the incomplete post. I’m a newbie and accidently hit post before finishing. Thank you for this forum and any help you can provide. I added more info but it wound up being a whole new post before I figured out this Quick Reply.
The 2 pressure switches in the front and the inducer were replaced and we had heat for a few hours. So, I checked it out myself. First I shut power offfor a minute and restarted it. The blower and inducer motor ran but no fire in the burners. I went outside and put my hand over the exhaust pipe blocking the flow for a few seconds. When I returned to the furnace the burners fired up and everything worked fine for a few hours. Then I have to repeat this process to get it working again. Also, I noticed an orange LED that blinks a couple times when it isn’t working. Is there a bad sensor that reacts to the exhaust pipe being plugged that would somehow cause the burners to fire?
All thoughts are appreciated.
 
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Old 11-23-18, 09:00 PM
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The control board is in the blower section. You can see the fault light blinking thru the door. Count the flashes. There is a list of the fault codes on the back of the blower door.

By you covering the vent..... you are messing with the vacuum on the pressure switch. Your tech should put a manometer on the pressure switch line and make sure it's where it should be.

The 2 pressure switches in the front and the inducer were replaced
Why ?? That sounds like a gun shot stab at repairing a problem. It could be a leak at the inducer blower.
 
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Old 11-26-18, 02:34 AM
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Thank you PJ - Turns out the orange LED is just the indicator when the igniter is trying to light. The red light on the control board is solid ďonĒ w/out blinking. Which I believe indicates AOK. Unfortunately, Thatís not true. Itís not AOK. Iíll have them check the pressure switch line and check for leaks in the inducer blower. If thatís not it, is it possibly the gas valve itself? Thatís about the only item thatís not new. Iím about ready to toss this furnace and replace the whole thing.
 
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Old 11-26-18, 07:04 AM
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I really don’t think it’s the equipments fault.
The problem needs to be diagnosed. Random parts thrown at the problem wind up with a situation such as the one you currently find yourself in.
It’s not that hard for a tech. Unfortunately a lot of residential companies are pushing for people that can sell over fixing anything.
 
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Old 11-26-18, 07:32 PM
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Had the same problem last week on a one year old furnace.
Three service calls and the problem was a faulty transformer.
 
 

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