Weird electronic pilot/gas control valve problems

I had 2 service men get stumped on my problem -- I'm hoping to educate myself a little before swapping parts or trying someone else out of the yellow pages...
Setup: Heil 7000 "Super High Efficiency Furnace" (about 13 yrs old) Symptom: Sometimes the pilot tries to light (click-click-click etc) but gas won't turn on.
The electronic pilot control valve has 3 wires comming into it -- I've been told these connect to sensors that tell the valve to shut down when a problem somewhere else is detected.
Tempory workaround: Wiggle/press down on one of the 3 wires and it turns on. You must wiggle it right at the terminal on the pilot control unit. Wiggle a little more and you can cause it to shut off.
The obvious first step was to check for corrosion and make sure the connections are solid and that the wires conduct and don't have breaks in them. They all checked out okay.
I usually kill power to the furnace (nearby switch is handy) until it shuts down before turning power on and wiggling/pressing on the connections. Occasionally just doing this will cause it to function normal, but not lately...
Tech#1 checked all the things that trigger the sensors, and verified the scenarios that would send shut down signals don't exist/the furnace is fine. Tech#1 even measured the voltage at each input to the gas valve during the time it was trying to light and verified the signal to the control box was good/as it should be.
The next logical guess was the little black electronic control box (on the pilot/gas valve) was faulty. Tech#1 contacted Heil and was told that this control box never goes bad, and if it had any problem it wouldn't work at all. He also said the only way to replace this little control box was to replace the entire gas valve, because even though the little black box unscrews you cannot buy it seperately from the valve. Ultimately suggested replacing both elec. pilot and the brain box.
Tech#2 witnessed the strange behavior, and quickly took to the "replace parts" strategy but could not provide a reason for the actual problem. Both techs had 15+ years experience, and said they had never seen this type of problem/short term solution before, and neither were convinced replacing the pilot/gas valve alone would fix the problem.
The problem is intermittent -- it existed the day I bought the house almost 3 years ago, and I'd have to wiggle wires a few times per night just to keep the house from getting too cold. Being late spring, I let the probel ride out until the fall, when I planned on fixing it. But in the fall, it worked flawlessly. It acted up a few time sin th spring. It was fine this winter until about 3 weeks ago, and now it's acting up numerous times per day. Sometimes the system seems to reset itself (all motors quiet down and stay off for a few minutes and then it fires up on its own. It was doing this frequently until recently and could maintain a stable temp in the house. But I got bit Sunday morning, waking to a cold house and had to intervene and wiggle/press down on the connections to get it to light the flame and fire up.
Has anyone else experienced this type of problem? It just seemed strange that both techs had 15+ years experience and said they had never seen this behavior before, and I wanted to make sure we were headed in the right direction.
Thanks Dave
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wrote:

Long rant snipped. First, make sure the condensate line is clear and flowing. If this doesn't work or if the line is clear then replace the gas valve.
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You need a new "wiggle valve" and so new "wiggle wires" that connect to it. Bubba
wrote:

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wrote:

I've seen something like this occur with a furnace in one of my places.
The draft sensor switch was intermittently shutting down the furnace. The chimney MAY have had a slight blockage with an old bird's nest. That and if the wind blew in the right direction or whatever would cause the switch to open and shut the furnace down. I say MAY because when I finally got up on a ladder to examine the chimney, whatever had caused it had fallen to the bottom.
Just because all the sensors were showing normal output when checked by the tech doesn't mean that they are either working correctly or not intermittently sensing a fault condition.
Most "pros" today don't trouble intermittent problems well. They, as in your case, either become parts replacers using the shotgun approach to find the problem or they walk away. There's no money in it for them to wait around or keep testing until the problem appears. Of course in all fairness, if they did, you probably wouldn't want to pay the bill...Seen it many times....
I actually enjoy challenges like this. My background is engineering and to me it's a problem of control system logic combined with detective work...
If it were my place, I'd intermittently bypass all sensor inputs until the problem cleared. Obviusly one has to do this under closely monitored conditions. One could get really high tech and monitor each sensor input to the control using a recording oscilloscope, but that's probably overkill... :-)
Doug
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wrote:

If you take this approach then please make sure your life insurance is up to date.
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wrote:

B.S.
You intentionally failed to quote the rest of what I had posted: "Obviously this should be done under closely monitored conditions".
What do you think I meant by that? Obviously, not to bypass the safties and leave the furnace unattended.
Doug
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Contact your local Heil distributor. Most Heil distributors have Technical Service Advisors ( TSA ) that are factory trained to solve field problems. They can assist a Heil dealer with service problems.
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