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Gas furnace won't lite

Posted: Mon Jan 24, 2011 3:47 pm
by sphoghead
I have a Ruud gas furnace that won't lite, Mdl. #UGL G 05EAUER, Ser. #DA 1 D302 F 08 94 3334. White Rodgers 36E37-214 gas control, Honeywell S9201A-1028 HSI & remote sensor. The ignition cycle seems OK, hot surface ignitor heats up, distinct "click" when ignitor reaches the right temp. but no gas. I tried to check the voltage, 24vac, across the valve and across the valve terminals on the IFC, but I'm not certain I tested the right terminals. On the IFC I tested across the wires I believe are coming from the transformer and got 28vac, on the valve I tested across the 2 terminals 3 times and read from approx. 22.8 to 23.6vac. I tested hot to ground once and read 24.2. Is this enough info for someone to determine the problem? If not I'll be happy to provide more info if I can.


- Gas furnace won't lite

Posted: Tue Jan 25, 2011 5:54 pm
by sphoghead
Thanks for the input, as for the value being "on", not this time, but have done it in the past and couldn't figure out why it wouldn't light. So no disrespect taken.
Here's what I've done today. Since it seemed the voltage to the valve was approx. 2vac low I jumped from the transformer to the valve and the valve opened, I could hear & smell gas. After clearing out the gas I ran the furnace thru a start cycle and it lit. It's been working find since.
What I have come up with is the furnace is 17 years old and the board and valve aren't working at 100%. The combination, low voltage and sticky valve, are causing the valve to fail to open. Thus I think they both should be replaced.
I'm open to any & all feedback on this.
Could the low voltage be a bad ground?
Thanks for your help.

- Gas furnace won't lite

Posted: Sat Jan 29, 2011 9:47 am
by nomadpeo
sometimes you can get a 'ghost' voltage reading that looks like a proper reading, but the circuit won't carry current. it will sometimes show up as a reading that is just shy of the rated voltage. your 22 v may be a bogus reading. as bigwheel pointed out, it could be due to a poor connection of ground or another connection. sometimes a missing or poor equipment ground can mess with these signals, especially on older models.

a valve sticking open is a dangerous situation. i can't recall ever seeing that. i'm not sure replacing the board is in order. the connections are more likely to be the issue with the signal. make sure you have the heat exchanger properly inspected by a qualified technician. i know it's hard to make sure, but the furnace is old and if you have a problem with the heat exchanger, you don't want to spend any more money on this equipment that is starting to have flaky problems with the electronics and other parts. everything has to be replaced eventually. maybe it's time. if you do, buy a unit with a lifetime heat exchanger warranty and make a comprehensive evaluation of the rest of your hvac equipment.