There is no spark sent anywhere on a Hot Surface System, there is not even a
device that creates a spark on the furnace. The HSI may need to burn up to
45 seconds before voltage is sent to the gas valve. Is there voltage to the
gas valve or does the sequence of ops end before that?

--
Bob Pietrangelo


www.comfort-solution.biz
On Time or Your Service Call is FREE
Preventive Maintenance Specialist

"Bill" wrote in message
ups.com...
Thanks for your informative and quick response, Greg.

Your description of my furnace cycle sounds exactly like what is
happening. I don't know, however, that I have never noticed a spark
ignition at the point the gas valve opens--even when it is functioning
normally. I do have a distinct orange glow, though, that seems to
describe a "hot surface ignition." That glow subsides at ignition or
ignition failure.

Gas pressure has been measured both at the point it enters the furnace
cabinet and inside the valve. Both pressures have read normally.

Is their a way to isolate whether or not the intermittent failure
occurs from the gas side or the spark side?

Thanks.

Bill