coleman furnace wont fire, but it does make spark and tick.

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Old 11-13-15, 03:55 PM
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coleman furnace wont fire, but it does make spark and tick.

so my parents have a old coleman (model number 2667A746) furnace. here is the exact sequence i observe.

model number of the gas valve is vr8450m2023, honeywell

i turn the t-stat to a high number (~90F)
i turn the t-stat heater switch to on.
exhaust gas blower goes on
some time passes (~30secs)
the thing starts to tick and make sparks (kinda like a spark plug, but constant. the ticking is the sound the sparking makes)
continues the sparking for ~30 seconds
stops sparking/ticking.
blower continues to stay on
i turn the t-stat heater switch to off.


am i supposed to heat a click as the gas valve enables? because i dont. is the spark supposed to be fairly large? it is not a large spark but its enough for it to make the full jump across the two leads. help please.
 
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Old 11-13-15, 04:18 PM
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something to add... the main blower never actually enables.

the blower i was referring to is for the combustion gas.
 
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Old 11-13-15, 06:36 PM
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You have an intermittent pilot ignition system.

Each time the thermostat calls for heat, the ignition control should turn on the gas to the pilot light and turn on the spark to light the pilot. When the ignition control board detects that the pilot light is lit, it turns off the spark and turns on the main burner gas.


So you need to check to see if the gas to the pilot burner is turned on.

Begin by checking to be SURE that you have gas to the furnace --- the meter turned on, the furnace shutoff valve on, the electric gas valve turned to the on position.

Turning the furnace shutoff valve off then opening the union or flex connector and briefly turning the gas valve on to verify that you have gas pressure is worthwhile. Be SURE you have gas to the furnace!

If you do, use an AC voltmeter to see if you have 24 VAC to the PV connection on the gas valve or ignition control --- you may need to disconnect the spark cable at the ignition control if the high voltage spark prevents you from getting a good voltage reading.

You can double check this by using a gas match or a match on a stick to see if you can light the pilot burner while the spark is operating.

IF you have no 24 VAC at the PV connection of the ignition control while the spark is operating, you have a bad ignition control which is failing to turn on the pilot gas.

IF you have 24 VAC at the PV connection at the gas valve and no gas, you have a bad gas valve .
 
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Old 11-14-15, 07:59 AM
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Seattle, thanks so much for the detailed help.

I understand what you are saying but what does pv stand for? I have attached a pic of the gas valve. which connection should turn hot when it's trying to open the gas valve? Or does it not matter because it's ac once I put the leads on each...

If the gas valve is bad, no biggy, swap out the gas valve.

If the ignition control is bad, I'd presume I just follow the wires back to the ignition control. am I swapping out the whole board?

Would there be any kind of safeties that are preventing gas valve from opening? or are the safeties all part of the start sequence?

Again, thanks for all the help.
 
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Old 11-16-15, 05:10 PM
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When the PV terminal is energized, the pilot gas electric gas valve should open and allow gas to flow to the pilot burner.

When the MV terminal is energized with 24 VAC, the main burner gas should be turned on aty the electric gas valve.

I recommend AGAINST DIY replacement of electric gas valves. Thery need to be adjusted to work with your furnace by someone who knows what they are doing.

However, it's quite rare to need to replace those gas valves. The ignition control is usually what fails between the two.
 
 

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