Two furnaces, at same time, both lost heat but still blow cool air

Lulu

Two furnaces.  One in crawl space, one in attic. Downstairs is set on a scheduled.  Upstairs is turned off as there is

enough heat from the lower level system and sleeping in on lower level.  





Yesterday, after returning from a day out, we noticed the temperature falling in the house as the day came to a close.  Normally the heat would be running and it would be toasty.  We manually bumped up the thermostat to force the heat to come on.  It did, but only blew cold air.  We then turned on the upstairs thermostat and noticed the same result.  No heat, just cold air.

Today my father and I looked at the crawl space unit, downstairs system, and didn't see anything obvious, nor anything that could make sense to affect both units the same way at the same time.  We checked the gas.  It was not having a problem heating the hot water heater.  We did some tests and smelled gas as expected when trying to force the furnace to fire.  There was a code 14 set by reading the blinking red light.



Both systems are Carrier 58PAV/RAV.  We turned off the breaker/power for more than 5 minutes (in fact we tried for 3+ hours) turned back on and still no heat.

nicholas bonham-carter

Blowing cold air

Usually the blower will not come on untill the burner has heated up the chamber, so that is unusual.

Many more experts are monitoring the "gas heat" section, so can you're post there for more replies?--NBC

Are they both controlled by the same thermostat? A problem with that could be the cause.

JStar

Furnace

That code is for ignition lockout. I would suspect a gas line shut down, but the water heater is working. My next thought is a common chimney or draft problem. Arethe furnaces sharing a chimney? Is there a valve on the gas line near the meter that only serves the furnaces?

Steve Whitbeck

HSI

You have two bad hot surface igniters.

The one on the furnace in the attic has been burnt out for a few days You just didn't know it because the crawlspace furnace was heating the house.

The HSI for the crawlspace furnace burnt out yesterday or today.

Make sure the service man cleans both flame rods too.

Lulu

Scheduled service...giving up

Thank you all for your rapid responses.  I'll address each one here:

Nicholas - yes it does seem strange that without ignition the blower starts up and will not stop blowing.  They each have their own thermostat.

JStar - I'll check for an additional gas valve, but since we did smell gas during our attempt to restart the furnace (per the manual) we ruled out the no gas theory pretty quickly.  That was our first thought, along with pondering why that could have happened in the first place as nothing had been touched or altered.  Both furnaces may very well be sharing the same chimney, I'll verify.

Steve - Actually, we had not even turned on the heat upstairs yet this season.  We rarely use that unit as our master bedroom is on the lower level, and yes, enough heat rises to make the second floor comfortable without additional heat.  I called service this morning and we'll find out the cause this afternoon.  It seems odd though that both furnaces are exhibiting the exact same symptom at the exact same time.



My only theory now is there may be a build up of dust/dirt in the furnace that is preventing ignition.  We recently did some sheet rock repair and sanding that filled the house with dust.  What's odd though is we only ran the lower system which cleared the air considerably.  We did not run the upper system, not even just the fan.



Again, thanks very much to everyone for input and advice.  This is a very helpful and responsive forum.  I'll bookmark for future!!

Lulu

Diagnosed

Upstairs system: 

Board is bad, must replace.  Not essential as we don't use the second floor much.



Lower system:

Bad ignitor, replaced, heating fine now.



Pure coincidence that they both went bad at the same time, or were discovered the same day.



Thanks again everyone!