Comfortmaker furnace won't fire

Scott Little

I have an 8 year old Comfortmaker sealed combustion furnace. The A/C works fine, however, the furnace won't fire. It does not start the firing sequence while in heating mode. I've checked the thermostat and it is fine and switches in heating mode, however, the furnace does not attempt to fire. Does this sound like a control board issue, or are there potentially safety switches that are preventing this from firing? It has had annual maintenance through 2008, however missed it lat year.

Marty S.

Scott, you'll need a meter to check voltages. Should be 24 volts between C and W on the furnace control board if it's getting a call for heat from the thermostat. From there the control board should send 120 volts to the inducer motor. If you have both of those but the motor doesn't spin take the flue pipe off and look for a dead bird or squirrel jammed in the inducer wheel.

Scott Little

Thanks for the reply. I applied 120 directly to the inducer and it sounded like there was a lot of water in the housing. I pulled it out, drained it and asked my 4 year old son if he sprayed water down the white pipe outside. He said he did it last week. Anyway, got the system dried out. Wasn't expecting that little twist...back to the issue at hand. I inspected everything and fired the inducer motor up again via extension chord and checked to make sure that both intake and exhaust were clear and working fine...not problem there...lots of flow and the inducer motor sounds fine. I obviously had a plugged drain and disconnected and cleaned all drain lines.

I disconnected all switches and jumped them out.

Result...no worky.

Voltage from the C to the W on the control board is low...almost zero with the thermostat calling for heat...set to 90 degrees F.

I tested the transformer that powers the control board and it is putting out 25.6 VAC...so that is not the problem.

I crossed the C to Y on the control board and the air fired, however, when I cross the C to W on the control board, nothing happens. That is really the only reason I haven't checked continuity on the white wire, and also because all connections look fine and we haven't had any major structural issues or anything happen that could have disrupted the thermostat wiring.

I am ready to order a new control board...do you agree, or do you think I may have missed something?

Thanks again for your help.

yuri

Take all the wires off the terminal strip and label them. Then put a jumper between R and W. That simulates a call for heat. Ventor fan should start running etc etc. If that works then you have a bad tstat or faulty wiring to/from it. Check if there are any error codes flashing on the gas valve or circuit board when trying to call for heat with that jumper on. Should be a legend of them on the back of one of the doors and in the manual.

Post the model# and pics of it. Lots of variations of that furnace out there.

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hvaclover

C to W ?!

Yuri direct short...blown fuse or the board got damaged by the water...

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yuri

Anything is possible when "jumpering" is involved.

Betcha it has the new "improved" idiot valve.

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kenmac

About time you caught that

Scott Little

Let's clear up a point where I mis-spoke...I jumped red to white at the board and got no repsonse, not C to W. I did check the voltage between C and W however, and there was none. When I connected red to yellow, cooling turned on. The induction motor seems to have survived the water...no birds.

The light on the Honeywell gas valve is a constant green. There are no lights or indicators on the control board.

The control board shows no signs as to ever having been wet and the fuse is intact.

The heating cycle does not kick in at all, the inducer motor does not start unless I supply power independently.

I will disconnect the wires as you mentioned and jump R to W again in the morning.

I had a spare stat from a former house and tried that with the same results.

Also, will get the model of the furnace.

Thanks again for your continued assistance.

hvaclover

What was my time coach?????????

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hvaclover

You have a bad Smart valve.

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Scott Little

I am not arguing the poetential for a problem with the smart valve, however, after looking it up (Honeywell SV9541) I found there were no error codes indicating any malfunction. Therefore the only potential is that a triac in the smart valve is smoked or the control board is done. The fact that the system turns on and works properly in cooling mode supports your theory that the smart valve has malfunctioned. Would it not, however, give some kind of error message if it failed internally?

BTW...I checked continuity on the White wire and the wire is sound.

Sorry to keep dragging this out...it looks like we're down to control board or valve.

Thanks to everyone for pitching in! Give me your votes and I will get on with ordering parts for the repair.

Comfortmaker - N9MP2075B12A2
Honeywell - SV9541
Control Board - ST9160B 1050

Thanks!

hvaclover

The valve controls inducer and ignition operation. The board controls only the blower for ac and heat cycles.

The valve has 24 volt and 110 volts supplying it. These valves are known for their frequency of break down and unpredictable false codes.

The voltages are/ will read unusual values.

You should have a dim-bright-dim-bright rhythm when normal.

You have a continuous 'ON" fault light. That is not even listed in the fault code directory.(as stated above Smart valve's notorious reputation for misleading fault codes)

In short your Smart Valve has become retarded. Time to replace it.

Warning: Be prepared for valve sticker price shock.

http://customer.honeywell.com/techli...it/69-1227.pdf

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yuri

Snoop thru here and you may be able to find a troubleshooting manual. Those furnaces are a huge pain in the azz to troubleshoot.http://gocomfortmaker.com/go/index.asp

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hvaclover

Ain't nothing in there to trouble shoot. That's what the honey link I provided was for.

There is not even a fault code chart in the those spec manuals on the site.

I do Heil and did alot of those stupid valves that are dual voltage. The OPs description of the problem is typical for this furnace and even Lennox Armstrong concord furnace line has a high failure rate with that valve. And the fault codes in most cases don't give a true story of what the problem is.
Of course even on systems with accurate fault codes, they are used only as a reference and the tech will use his experience and accurate test reading to discover the truce cause of failure.

I had one recently that kept flashing a closed press switch before ignition.
I worked around the the false code and discovered it was the valve dropping out the ignition so quickly it fooled it self into a false flash code.

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yuri

I do 80% Lennox and 20% of the other brands. Don't run into many of them and never liked them when I did. Just have to slog thru them when I do. Very little Armstrong stuff up here.

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