furnace not getting house up to temp: suggestions?

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Pretty much agree with what you've said. I never had a thermocouple fail in the decades I had them. Never had a furnace fail to light and heat. The "new" furnace I had put in 13 years ago (Rheem) failed multiple times, once because the igniter failed, which can be quickly remedied if you keep a spare on hand. It's a 6 buck item on mine. Same could be said of a thermocouple.
The other times were caused by a flaky motherboard, and I always got it started by cleaning the flame sensor, though that was probably a motherboard related fluke too. Since the motherboard failed with a sticking fan relay and I had a new motherboard put in a few years ago there hasn't been a glitch with anything and I haven't touched the flame sensor. But he put in a the new flame sensor that came with the motherboard.
Besides it being almost the coldest day of year, the first time mine failed was on Christmas Eve! Lots of cursing about the furnace.
Anyway, I had this one put in, replacing the original pilot light/theromocouple furnace because I went to central air and had to replace the old one because of that. Went with an 85%, mostly because I was told the higher efficiency furnaces were even more prone to failure.
I recommended the OP think about replacing his furnace because it already has the motherboard and sensors, and is 15 years old. It's an option to think about if he can get good HVAC advice. But I didn't know what you said about cracked heat exchangers and carbon monoxide, since I had drunk the Kool-aid on that. So I kind of take that part back, though if you *do* have a leaky heat exchanger there's reasons to think about replacing the furnace.
When I had the motherboard replaced I asked the HVAC guy about getting the evap coils cleaned. He said something like "If the A/C is working like it always has been, it's not worth getting in the plenum to clean them. Wait until it's a problem."
--Vic
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On Fri, 3 Dec 2010 05:08:43 -0800 (PST), snipped-for-privacy@optonline.net wrote:

of my furnace by about 25% - and I don't mean incremental - like it's 80% now so you need to increase it by 25% (25% of 80) to 100% - I mean it's 80% now, you need to go to (80+25+)105%
Ain't gonna happen in this world. And mine is better than 80%.
Last year heat (including water heater) was about $700.
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On Dec 3, 2:14 pm, snipped-for-privacy@snyder.on.ca wrote:

The $200 a year in fuel savings was predicated on Home alone Guys 34 year old furnace, built in 1976, which he holds so dear. It has nothing to do with your furnace, unless you think it's likely a furnace built in 1976 is getting over 80% efficiancy like yours.
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On Fri, 3 Dec 2010 11:25:58 -0800 (PST), snipped-for-privacy@optonline.net wrote:

years ago, and my gis bill didn't change at all. I did save some on the hydro bill.
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If it is the overheat sensor realise what can cause overheating and ruin your unit,reuuced airflow from a clogged AC coil, poor or blocked ducts, Closing off registers, a bad gas assembly allowing in to much gas. The heat exchanger has a design temp range it can safely operate at. Go higher than that temp and most exchangers fail fast. You start by checking the AC coil to see if its clogged and air temp just above the heat exchanger. If you never had it cleaned and checked out by a pro now is a good time.
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To update on the advice people have suggested:
I think I can pretty much rule out thermostat issues. Got up this morning - 60.5 degrees when the thermostat is calling for 70, and no furnace action. I took the covers off the side to see if there was any obvious issues, and pretty much not knowing what to look for put the covers back on. As soon as the lower cover tripped the switch (that prevents the furnace from firing up while the cover is off) the furnace immediately began its pre-heat cycle (fan to clear the air cap in the stack, glow of the ignitor, etc.), fired up and brought the house up to temp.
Weird. I don't know what re-set, but it's been fine all morning and afternoon (working from home today).
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wrote:

Perhaps the lower cover was loose and vibration was tripping the switch?? Stranger things have happened.
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wrote:

To update on the advice people have suggested:
I think I can pretty much rule out thermostat issues. Got up this morning - 60.5 degrees when the thermostat is calling for 70, and no furnace action. I took the covers off the side to see if there was any obvious issues, and pretty much not knowing what to look for put the covers back on. As soon as the lower cover tripped the switch (that prevents the furnace from firing up while the cover is off) the furnace immediately began its pre-heat cycle (fan to clear the air cap in the stack, glow of the ignitor, etc.), fired up and brought the house up to temp.
Weird. I don't know what re-set, but it's been fine all morning and afternoon (working from home today).
My evil side forces me to ask this:
Do you have to remove that lower cover to change the filter?
Colbyt
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[snip]

Doesn't sound evil…it would be perfectly logical to assume that the filter could be clogged enough to overheat the unit and cause it to shut-down (or whatever the HVAC term is for an hours-long standby) and that the cover switch could reset that.
But, no, the filter is on the side of the unit where the cold air return duct enters the furnace.
Furnace is back to acting up again, but I've taken notes from what people have said here, and will ask the tech when he comes tomorrow morning (when it's 61° and the thermostat is blinking angrily, demanding 70°).
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I'm sure someone already covered this, but I've had this happen to me a few times. What I think is happening is that the furnace doesn't actually light when the thermostat calls for heat, and after three cycles of not lighting it shuts off. Might be a dirty flame sensor, but I actually suspect that it is an insufficiently shielded intake or exhaust pipe that is allowing wind to actually "blow out" the flame. Seems to only happen to me in very windy weather, and maybe only once a year.
nate
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responding to http://www.homeownershub.com/maintenance/furnace-not-getting-house-up-to-temp-suggestions-607727-.htm egonzo50 wrote: I'm not an expert service agent nor do I claim to be. I hope my story will help and I hope I got to you b4 u spent money on a service guy. Anyway....I have a Goodman furnace and I experienced a similar problem. The furnace would shut off prematurely and I'd wake up to a cold house. The problem with my furnace was the 'flame sensor rod' (google flame sensor rod for picture/ur unit). The rod is true to its name....it lets the unit know when it reached ur set temp. I learned that this rod never goes bad although u will be told otherwise hence spending money. On my unit...it is held in place by one screw. Remove the screw and unplug it (Of course...make sure to turn off the power to the unit...better being safe than sorry). Now...with sandpaper...clean off the rod. Put the sensor back with the one screw and plug it back in. Turn the power on and now check if the problem was solved. Approx. 10 minutes worth of work...if that. Hope it helps. Good luck!
Kyle wrote:

------------------------------------- | | | _ | _________|__( )__|_________ x/ _| |( . )| |_ \x |_| ---*|_|
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Resolution!
Despite the fact he posted from the spamming site, one of the last to reply to this thread (he shall remain nameless so as not to encourage the parasites of Homeowners Hub) actually was onto the solution.
The HVAC company sent out another tech who checked the draft valve diaphragm (is that the right term?) that detects if the stack has a draft. It seemed to be OK, but he thought the hose might have been a bit loose. The second thing he checked was the flame sensor, which had some significant carbon build-up. He cleaned it with some ultra-fine grit sandpaper (if you do this yourself, do not use anything below 200 grit!) and everything is peachy, er, toasty again!
The good news is that the tech said this should have been done when the previous tech had done a service cleaning, so there was no charge for this service call.
The better news is that he taught me a few things about the furnace, and I'm planning on having one of the newer silicon hot surface ignitors on-hand for when my current ignitor cracks, as it will inevitably do, so that I can take care of the problem myself!
Thanks to all who posted for your suggestions and feedback!
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That is better news. When you wake up freezing on a Sunday morning, it is good to know the basics and what to look for. Amazing how many people have no idea where a reset is. Ask any oil service guy how many times he's been called out to find that someone accidently turned off the upstairs switch.
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