Heil gas furnace sometimes won't ignite
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!
what are the numbers on the smart valve? there is a number stamped on the side of the valve which indicates the date made. Some of these were recalled several years ago. Does it have an on / off switch or a twist knob for turning the valve on and off?
Does your furnace have a differential pressure switch? If you are getting exhaust blower to come on, did the repairman check the pressure switch to see if it had enough differential pressure to close it?
Agree, have someone check the pressure switch with a manometer and see if it is drawing. Also check the hole where the vacuum switch tubing connects to the "little blower". Lot of times the hole will partialy blocked with rust and crap. Use a very small drill bit or piece of wire to clean it out. Intermittent problems are the worst to fix, that being said changing the filters is just a moron fix. "gee the car won't start, I know let's change the oil and wash the windshield, that should fix it"... LOL
"Go big or Go Home"
Thanks for the great replies!
The smart valve # is HW SV9500M2674. Below this number is stamped 9543 22. It has a twist knob, not an on/off switch.
Yes, the furnace has a pressure switch. I probed the hole with a wire where the vacuum tube from the pressure switch goes into the blower. I'll have to run the furnace thru a few cycles this morning to see if that might have been the problem.
At another forum, I was advised to try gently sucking on this vacuum tube when the furnace fails to ignite, in order to ensure that the pressure switch is closing. I'll try this the next time it fails to fire up.
I'll report back to you all when I finish my testing today. Thanks again for your input.
I have a Heil furnace as well and I have had this problem on 2 occassions.
I would open the combustion chamber up and check the ignition sensor - it's a small rod that's about 2 inches long and lives to the side of the ignitor. It's held in place by a 1/4 inch sheet metal screw. Remove it (don't drop that screw!) and wipe it down with a little steel wool. Crud gets on there and can fool it into thinking ignition isn't happening.
It could also be the ignitor itself which you may have to replace (I keep a spare one on hand since I go through one every 4 years or so and it always gives up on the weekend in the coldest day in January.)
If you mess around with the ignitor - be sure not to touch the ceramic since it's sensitive to oil and moisture of your hand and will shorten the life of it - much like a Haligen bulb.
I suspect it's your ignition sensor and would start with that.
Needless to say shut off your power to the furnace at the breaker BEFORE you open it up.
I can't find the recall notices but that is close to the date range of the valves that gave so much problem. I have seen some of the older heils with the little ports stopped up and not proving the air flow switch but would be more inclined to think that the valve is causing you problems.
Reminds my of my stove top igniter. When I haven't used it for a few days it can take a while to ignite.
A bulletin was issued 1997 and expiration date was 1 May 2000. Affected Smart Valve was SV9500 with date code 9426 to 9547 so it does appear that you have this valve. This is on Customer Assurance Technical Tip #493 issued 1 June 1997. If you would like a copy of this please give me your e-mail or fax, mine is in profile. While this may be your problem, it does state that any claims for warranty would be denied after the expiration date of 1 May 2000.
If the furnace does not try to ignite, it is NOT the flame sensor. I suspect that you will find that it is the smart valve. I would still like to see someone verify that it is not the vacuum switch.
"Go big or Go Home"
BlackAdder wrote "if the furnace does not try to ignite, it is NOT the flame sensor." Yes, this makes sense to me.
As I wrote earlier, I cleaned out the hole where the vacuum tube connects to the "little blower" (BlackAdder's suggestion). Since then, I've had 4 or 5 straight successful ignitions. That's encouraging, but I'll need to see about 24-36 hours without a failure before I can break out the champagne.
If that doesn't solve the problem, I'll move on to sucking on the vacuum tube and then the ignitor or the "dumb valve".
I can't tell you what a relief it is to contact such a bunch of knowledgeable, generous experts as you all, after a month of frittering away countless hours on this and wasting $$$ on clueless local HVAC companies.
I'll keep you posted....
I think I'm finally getting close to the source of the problem.
After I cleaned out the orifice where the vacuum line goes into the draft inducer, I had 24 hours of perfect performance from the furnace, with maybe 20-30 consecutive successful ignitions. In the previous month, I've never seen it work properly through more than 6-7 cycles.
I thought the problem was fixed, but then the thing failed to work two times yesterday morning. Each time, I pulled the vacuum hose off the inducer and sucked on it. There was an immediate click from the pressure switch and after fiften seconds the furnace ignited. Eureka!
After a few successful cycles, the furnace again failed to ignite. This time I decided to try something different. I pulled the condensate drain hose out of the condensate pump and blew on it. I heard a gurgling sound, the pressure switch clicked, and the furnace ignited.
So, it seems that the basic problem is that the draft inducer is sometimes failing to provide enough vacuum to trip the pressure switch. Now the question is why is this the case?
I noticed a couple things: First, the drain hose going into the condensate pump was curved into the shape of a p-trap. I recalled that when I replaced this pump a while back, it didn't line up with the furnace like the old pump, and I had to distort the condensate tubing in order to get it to fit into the hole in the pump. Second, where the flue pipe sticks into the draft inducer, the silicone cement has failed - you can easily pull the flue pipe out of the inducer. Even so, it fits quite tightly into the inducer.
I've pulled the drain hose out of the condensate pump and just let it hang straight down toward the floor (outside of the furnace, of course). Any water that comes out will find its way to a nearby drain. I'll buy a longer piece of tubing so that I can run it into the condensate pump without putting a crook in it. Is it important to replace the silicone where the flue pipe goes into the inducer? Do I need to figure out how to remove the condensate drain and clean it?
Again, many thanks to you guys for your valuable advice!
About a year ago I ran into a similar situation with a honeywell smartvalve. Still haven't figured why they call them smartvalves. I ohmed everything, checked gas pressure, pressure switches ect. Intermitten ignition just as you've described. What I finally discovered was one of my pins on the wiring harness to the gas valve had backed out just enough to cause the problem. Felt like an idiot considering the time I had spent on the call. I ate about two hours labor. I repositioned pin firmly into harness and no more problem. Later I found out through the grapevine that the home owner had hired another company to diagnose problem and had to pay 8 hours labor with no result. Since my repair several techs have told me they've run into the same problem. Maybe it's a long shot but it might be worth checking out that harness. Good luck