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Discussion Starter #1
Our gas furnace will not come on. Fairly new Honeywell electronic thermostat. I tried resetting it by shutting off breaker for HVAC, but to no avail. Relay in thermostat does click when you set it to heat. So I shuffled into crawl space to see what I could see. Looks to me like photo I took is only available access. Vent and intake hoses on other side.

This system looks like someone put some time and money into installing it, as it has separate thermostats for upstairs and downstairs. All vent hoses going to it are well-insulated. I don't know how they got this unit under house, because crawl space door is only about 3' x 3', and house is split-level.

I know I am not going to be able to do anything with this, but I am wondering what HVAC guy will not crawl under there and say "How the heck do you expect me to work on this?"
 

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That’s a zoned system. The controller you mentioned is the zone panel.
Crawl spaces are part of the trade. They aren’t fun but techs are used to them.
That vent pipe isn’t installed properly.
 

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Discussion Starter #3
Heh, vent pipe installed incorrectly doesn't surprise me, especially with some of the other problems we've had with this house, like some improper wiring. I am handy with tools, being a mechanic, and do a lot of DIY repairs on house. But this is a natural gas system, and I will leave it to the pros.

Can you tell me how the two separate zones work? I guess I mean is there some kind of heat/cool blend door like in a car that lets you maintain two different ac temperatures upstairs and downstairs?
 

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No, there are zoning dampers upstairs and down. The zone panel takes thermostat inputs from both stats and uses them to control the equipment. The system still cycles on temperature setpoints. No blending.
 

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Discussion Starter #6
Tech said some small tubing connected to a vacuum switch that detected airflow got chewed in half by a rat. I couldn't find panel because it was surrounded by ductwork. Tech said he couldn't understand why they didn't turn unit the other way so panel would face taller part of crawlspace. He did the repair, checked the burners, and had it fired up within fifteen minutes. For which I paid bill ($120) and handed him a $30 tip. He earned it.

I told him someone told me exhaust pipe wasn't installed correctly and he said he didn't see a problem as long as exhaust was exiting roof, which it was. Roughneck, can you tell me what's wrong there?
 

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The venting is laying on the plenum insulation. B vent should have a minimum of 1” clearance. The venting is also pitched down and then pitches back up, and appears to have a very long horizontal section. The inducer isn’t there to push exhaust all the way outdoors, just to induce the draft through the furnace. The venting must provide adequate draft to deal with the products of combustion.
I’d be very curious what your draft numbers were.
 
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