New 100,000 80% Heil furnace put in 12-19-1997 - no heat coming out of the vents.

Diagnosis from 2 different people was :

1. trace the wiring from the thermostat and the blower, because the blower works, but there is no heat so somehow the thermostat is not sending the message to the furnace.

How do you trace the wiring? I cannot follow it all the way due to the stainless steel ducts down by the furnace plus the water heater is there too, which leaves zero room to squeeze in even for my skinny body.

2 Replace combustion blower motor.
The combustion motor was changed and it still has same problem.

5. thermostat also replaced and same problem.

6. Now furnace will not turn on!

I live in Alaska and need some feedback soon please. We have snow, and you never know when temps will drop more.

1st thing,at the furnace tie together or jumper the white and red tstat wires. This will bypass the tstat and the wireing going to the tstat,if the furnace goes through the cycles and operates OK (except it won`t cut itself off) you will know the furnace is OK and its either in the tstat or the wires going from tstat to furnace,, let us know

I already have done what you suggested and the furnace did go on. Then my husband replaced the blower combustion motor and the thermostat and now the white wire into furnace, and on other end by thermostat have no voltage. (checked it with a voltage meter). We also replaced a broken fire igniter (smart valve).

I think we need to replace the thermostat wires. It is 18 gauge , 3 wires white, red, and green. I found this out by telling the guy at Lowe's what I needed. Now somehow we need to figure out how much wire is needed. So I am going to go and guess where it is going from furnace to thermostat in order to get the required length of wire. Hopefully this is all that is wrong!

Have you check the transformer? Should have 120 volts going in and 24 volts coming out,, the transformer is where the voltage comes from that goes to the tstat,, red wire if wired correctly

What is the transformer and where is it located?

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Originally Posted by sun1

I already have done what you suggested and the furnace did go on. Then my husband replaced the blower combustion motor and the thermostat and now the white wire into furnace, and on other end by thermostat have no voltage. (checked it with a voltage meter). We also replaced a broken fire igniter (smart valve).

I think we need to replace the thermostat wires. It is 18 gauge , 3 wires white, red, and green. I found this out by telling the guy at Lowes what I needed. Now somehow we need to figure out how much wire is needed. So I am going to go and guess where it is going from furnace to thermostat in order to get the required length of wire. Hopefully this is all that is wrong!

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If you already jumped are and w at the furnace and it worked fine, then your problem is definitely either in the thermostat or wires. Try jumping are and w at the termostat. If it works you have a bad thermostat. If if doesn't you need to replace the wires. Like I said, if you have jumped are and w at furnace and its works fine, then you have eliminated any problems with the furnace itself. Guaranteed the thermostat or thermostat wires will be the problem. There was most likely no need to replace other parts (combustion motor, or igniter).

Sorry but you need to call out the pro`s,, I`m sure if you don`t no what a transformer is you won`t be able to test it to see if its working... do you have a multi-tester? If so can you check the hot/red wire going to your tstat for low voltage? If you don`t have around 24 volts you either have a bad transformer or bad/broken wires

OK ,mygirlesdad is right,, I overlook the fact that the furnace was working with wires tied together.If it indeed did start and run your wires should be OK also

I assume you jumped r and w at the furnace, not the thermostat. If you jumped it at the furnace and it worked, your thermosat wires may still be the problem. Need to jump the wires AT THE THERMOSTAT now to see if its you thermostat , or indeed your thermosat wires. Good luck .

The wiring to the combustion blower is OK, but there is no voltage, ohm's to (panel) control board.

Well, you have me completely confused. Lets start over. What is your problem. What does the furnace do. Did it work fine when you jumped are and w , then you replaced the draft inducer motor, and now it doesn't do anything when you JUMP R AND W AT THE BOARD. It will really help us to help you if you answer the questions we ask. We are hear to help, but we have to have information in order to do that. I promise that if we could be there and actually put tester to controls we could have this fixed in minamal time. But we aren't there. We really want to help, but we can't unless you answer ours questions. If you aren't sure how to answer, then I really do recommend calling for onsight assistance. They should be able to fix your problem and you will sleep better at night. Good luck.

What is your problem. What does the furnace do.

Problem : no heat, furnace will not come on.

Did it work fine when you jumped r and w , then you replaced the draft inducer motor, and now it doesn't do anything when you JUMP R AND W AT THE BOARD

Yes , after replacing combustion blower motor and igniter, and thermostat it does not jump r and w at the board.

Ok, once again jump r and w at the board, then while it is jumpered, check for 120v to the combustion blower. If there is voltage, your new draft inducer(combustion blower) is either stuck, or bad.

The first thing that should happen when you have a call for heat(meaning r and w are connected) is the combustion blower should start to run, if this isn't happening, you either have a power problem to the furnace, or a bad control board(or blown fuse on control board), or a bad combustion blower.(possibly faulty wiring aslo)

Did you check and see? There`s a plug-in type automotive looking fuse in some control boards, some are hard to see

If the inducer motor will run but the ignitor will not glow, you need to check for voltage going to the ignitor(It may be out) or for a pressure switch sticking.