I have a Heil gas furnace, about 12 years old. For the past month, the furnace has been failing to ignite consistently. After receiving the heat signal from the thermostat, it usually runs properly, but about 25% of the time it doesn't - the little exhaust blower in the furnace starts up, but nothing at all happens in the combustion chamber, and of course the fan does not start up. The little blower just keeps running. Once this happens, I have to turn off the heat at the t-stat and give it a rest of about 15 minutes. When I try to fire it up again, it will still fail about 25% of the time.
I've had three repair guys out to look at it. The first one told me to replace my filters, but this didn't solve the problem. The second said the furnace was fine, but I needed to replace my old t-stat. I did so, but this had no effect.
The third guy seemed smarter. Unfortunately the furnace fired up properly each of the 6 or 7 times we tried it while he was here, so I couldn't show him the problem. His opinion was that most likely the smart valve was malfunctioning, due to poor or corroded connections inside the valve. He suggested that when the problem occurred, I should wiggle the wires going into the smart valve to see if I could force a connection, allowing the valve to send the needed signal to the combustion chamber. I've tried this several times, but with no positive results.
Well, I've now spent $200 on repairmen, but no progress has been made. I understand a new smart valve would cost about $200 plus labor, and it's not really clear that this would fix the problem. Any suggestions on what the heck I should do next would be much appreciated!