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despatchted · Apr 8, 2009, 01:12 PM

I have a bryant model 395A furnace that was installed in 1986. The pilot briefly lights and then goes out. There is a 646A-X gas valve for the heater. When I turn the thermostat on I get a solid 24 VAC Between terminals 4 and 3 with intermittant pulses of 24 VAC between terminals 5 and 3. The pilot turns on briefly every time there is a pulse between terminals 5 and 3 and then fades out. Is this a problem with the valve?

mygirlsdad77 · Apr 8, 2009, 03:42 PM

KC13, where are you?? KC is a pro on bryants. I think you may have a bad ignition module. I really don't think the gas valve is your problem. Can you tell me what your ignition module looks like?

farfield · Apr 8, 2009, 03:51 PM

Originally Posted by despatchted

I have a bryant model 395A furnace that was installed in 1986. The pilot briefly lights and then goes out. There is a 646A-X gas valve for the heater. When I turn the thermostat on I get a solid 24 VAC Between terminals 4 and 3 with intermittant pulses of 24 VAC between terminals 5 and 3. The pilot turns on briefly every time there is a pulse between terminals 5 and 3 and then fades out. Is this a problem with the valve?

Sorry I thought the 395 was always a solid ignitor - HSI Hot Surface Ignitor. Is this a spark type ignition?

Check for voltage at your draft switch (assuming it has one all the 395's Ive sold have one but it may be older than what I sold:rolleyes:

Joshdta · Apr 8, 2009, 05:18 PM

I would agree with mygirlsdad. Is your spark box a grey s86u box? If so odds are you need a new one

mygirlsdad77 · Apr 8, 2009, 05:29 PM

Des, maybe you can post some pics of your furnace controls... it will help us isolate your problem.

despatchted · Apr 9, 2009, 09:55 AM

Thanks for all your replies. It was a problem with the gas valve - the coil for the pilot hold circuit was actually burned out - the pickup coil was OK so that's why the pilot would lite and then go out. Obviously this would never allow the flame detector to lite the main burner.

mygirlsdad77 · Apr 9, 2009, 03:09 PM

Interesting. Glad you got it fixed, good job.

jad69 · Oct 30, 2010, 10:48 AM

I have a similar problem. Bryant model 395A furnace that was installed about 1983. Full model 395AAW036055The pilot briefly lights but the spark generator keeps cclicking, then pilot goes out in about 30 seconds. The spark generator clicks twice as fast if the pilot is not lit, so I THINK the pilot flame detector is OK. It has a Model 646A-X natural gas valve in it and I want to see if the coil for the pilot hold circuit is OK. Valve has 5 connections. One connector has Blue,Brown,Green. The other Blue and white. Since Blue is common I use that for reference. When off Brown connector measures 215 ohms and green 22 ohms and white 20 K ohms all WRT blue. When trying to start green measures 26 VAC, brown 47VAC (! ) and white zero. What do I need to replace to fix this heater and why? Thank You!

farfield · Oct 31, 2010, 07:33 AM

The spark keeps on sparking indicates the sensor is not sensing through the flame of the pilot. I have found a claening of the semnsor fixes over 90% of these problems. Remove the spark and sensing assy. Take emery cloth or fine sand paper and brush - clean the sensor. Careful not to spread the electrodes on the spark assy. The problem could also be a bad ground. If this is the trouble removing the sensor and look for corrosion or stain on the base or around it. Wouldn't hurt to clean this mounting area with the sand paper either. Then replacing it see if your flame is covering the sensor.

I was told that the spark continues even if the flame is established its just going through the flame to ground and you can't see or hear it. So it may not have the flame where its needed.