Furnace only "clicks", won't start

Problems related to residential installations.

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Freon
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- Furnace only "clicks", won't start

Post by Freon » Sun Feb 08, 2015 9:49 pm

Your flame sensor rod is the electrode for the spark ignition. The spark travels from the electrode to the pilot frame that is grounded by virtue of its mechanical connection to the furnace frame.

Your first task is to determine if you have spark during every ignition attempt. If you do and there's no pilot then you may have a gas valve issue.

If you don't have consistent spark then you may have a bad control board (high voltage section) or the gap between the electrode and pilot frame is too great.

You need to watch and listen. Once you have a consistent pattern of misbehavior, you can determine the most probable cause.

LennoxHVAC
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- Furnace only "clicks", won't start

Post by LennoxHVAC » Mon Feb 09, 2015 10:22 am

Always turn off power to the unit before removing the front panel.
Practice safety.

If there is power to the unit, NO pilot flame means several things.
Have it checked, I could be a simple 10 minute diagnostic.

joezappp
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- Furnace only "clicks", won't start

Post by joezappp » Tue Feb 10, 2015 2:39 am

Thanks, Freon. Got it, got it, got it, and got it. Thanks so much.

I guess the problem is that I'm not getting consistency anymore, which could mean I have more than one issue. Here were my observations -

Tonight I observed the unit with six separate flicks of the thermostat switch. 4 of the attempts were just the "click" and ensuing "buzz" or "hum". I did not observe a spark. On 2 of the attempts (the 2nd and 5th attempts) the flame lit and quickly went out, followed by the automatic attempted "click" to relight to no avail. It only re-attempted once each time. Obviously a spark was initially present those times for the pilot to light. I did not see it, probably because it happened so fast. Still, in the end, I should have seen sparking even when the pilot wouldn't light, and I didn't see it. Should this spark be fairly obvious? Or is it merely a faint spark that would be easy to miss? Also, if my end result is the same as I witnessed tonight...that is to say that sometimes I get a spark and sometimes I don't, and when I get a flame it quickly extinguishes...it would seem that fixing one issue wouldn't fix the other, as it would seem that I have 2 separate issues. Correct?

Also, am I correct in saying that the control board is my S86 module?

I should point out that the wire to the pilot assembly on my unit is a very thin wire. It's not thick at all. Also, to me it looks bent at a sharp angle, a bit black, and a bit frayed where it connects to the screw near the pilot. Maybe it's normal due to it's location near the flame, but I wanted to share it in case it's not. Thanks...

Lennox, I understand that ideally we don't want the front panel off when the power is on, but how on earth do you troubleshoot it then? I'm sure it's a 10 minute diagnostic for a pro. Everybody has to start somewhere. There is a learning curve with everything. I've learned quite a lot about the mechanics, functions, and inner workings of this unit and it's parts just in the past few days. Prior to that it was a mysterious box that I hoped wouldn't break, and I would get to know it on occasion by changing the filter and vacuuming some dust...

LennoxHVAC
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- Furnace only "clicks", won't start

Post by LennoxHVAC » Tue Feb 10, 2015 9:37 am

Honeywell S86 is your pilot control module.

The gas supply for pilot is a suspect at this point.
Not sure if there is a toggle switch to restore gas supply for pilot.

Were the flames at 2nd and 5th at pilot or burner?

Freon
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- Furnace only "clicks", won't start

Post by Freon » Tue Feb 10, 2015 1:40 pm

Here are some things you can do. First I would very carefully check the wire from the S86 control board to the pilot assembly. It's a high voltage line and it's possible the insulation in places might be weak. As a result you'll get sparking from another place along the wire and not at the intended electrode. You need to verify consistent spark. You should be able to hear it. With the lights out you should see it. You can call for heat at the thermostat and then switch the furnace on/off at the furnace location. Get someone to do the switching while you observe.

With the power off, you can disconnect the wires from the gas valve. MARK/LABEL each wire so you reconnect easily. Tape the bare wire ends. Now you will not hear the pilot portion of the gas valve click. All you should hear and see is the spark. If you do not have consistent spark for at least 5 seconds then your high voltage wire may be bad or the porcelain insulator of the spark electrode may be cracked. Be sure the high voltage wire is not close to anything metal, if possible. It's the same as car spark plug wires on a very moist morning arcing to the engine block before getting to the spark plug. Wire insulation does age.

If you prove consistent spark, that will eliminate one possibility. Reconnect the gas valve and observe the pilot lighting, or not. Possibly there is some debris in the pilot tube. You may need to remove the assembly and check. The gas valve may be giving good flow but the debris is causing the flow to be diverted away from the spark.

Also you can try the following. When you call for heat and you hear the gas valve click (you should know that noise by now as compared to the spark click), take the wooden handle of a hammer and gently tap the gas valve body. Possibly the solenoid isn't opening the pilot port 100%.

If you see the pilot light and then extinguish immediately then you're back to the flame sensing circuit of the S86. Either the electrical connections are not good enough or the S86 is old and tired and not capable of sensing the current flow.

This process to find the exact cause is tedious. But it's less expensive than throwing parts at the problem. In thy getting, get thee understanding. You'll be a furnace pro after this episode.

joezappp
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- Furnace only "clicks", won't start

Post by joezappp » Wed Feb 11, 2015 10:50 pm

Thanks Lennox. The only flames I've seen are at the pilot. I'm unsure about a toggle switch for pilot gas supply.

Freon, you are REAL good. You are a thorough troubleshooter, and really know your stuff. I am going to try all your steps. I really appreciate you sharing all this knowledge with me. I'm really coming to understand how everything in the unit operates. Too bad I'm getting no consistency at the unit.

Before I ask about some of the steps you describe, let me share what I witnessed tonight, which I hope helps a bit more. Tonight I repeatedly got a pilot flame on the majority of my first 12 tries. I never saw the spark...I think it's well hidden inside the bracket...but I sometimes HEARD sparking. The flame would stay on for 2-10 seconds and go out. I sometimes heard sparking/crackling before the flame would go out. It sometimes re-lit, and other times would just time out. After the 12 tries, I could no longer get a flame. Just the click, followed by the ensuing buzz and hiss. I could find no evidence of sparking. Doesn't mean that there wasn't, but I couldn't see any sparking, and I heard no sparking.

I put my multimeter on the PV and MP/PV connections of the S86. It reads 27 volts. I read that it should read 24, so it's in the ballpark. I thought it might help us? .

The high voltage spark plug wire looks and feels normal. Anything else I can do there?

I'd be interested in examining the pilot assembly to see if the pilot is plugged, and to see if the spark plug looks damaged in any way. These are located inside a small black bracket. I don't know if the bracket actually holds the assembly, or if it just shields it. Please advise on how to remove the assembly, what to look for at the assembly, and how to reassemble. Thanks so much, as always.

Freon
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- Furnace only "clicks", won't start

Post by Freon » Thu Feb 12, 2015 3:34 pm

If the pilot flame is a solid blue color (no orange) you're probably OK with the flame.

One question. Since the sequence is spark, pilot port in the gas valve opens, pilot flame makes, flame sensor verifies pilot flame THEN main gas port opens. My question, when the pilot flame was ignited before it went out (you said between 2 and 10 seconds), did you ever hear the main gas port in the gas valve open? It would be a definite metallic click. You would also hear the gas flow to the main burners.

If you did not hear the main gas port open then you're back to the flame sensing circuit. It's either failing due to the pilot assembly being dirty or it's failing due the the control unit (S86). You can try removing the pilot assembly and giving it a thorough cleaning especially the spark electrode. Then see what happens.

joezappp
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- Furnace only "clicks", won't start

Post by joezappp » Thu Feb 12, 2015 7:03 pm

Thanks, Freon. I did not hear the main gas port open, so I am going to google how to remove the assembly, how to clean it, and how to properly put it back together. I don't want to screw this up. Thanks to your help, we're getting closer to the malfunction. I'll be back in touch when this is done...

joezappp
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- Furnace only "clicks", won't start

Post by joezappp » Fri Feb 13, 2015 1:49 am

Hi Freon. I removed a pair of access panels so that I could get to the bracket screws to remove the black bracket that shields the pilot and electrode apparatus. Once the black bracket was removed, the apparatus hangs with very little play due to the gas tube/pilot tube. Please guide me from here. For starters, I believe that the gas tube/pilot tube must be removed to get complete access to the apparatus.

1) If I'm indeed correct that the tube must be removed, how do I safely and correctly remove it? Simply with a wrench?

2) How do I safely and correctly reinstall the tube? I suppose that is to say, will I need to be concerned that gas will leak out of the connections?

3) Is it imperative to turn off the gas valve, or did turning the furnace switch off suffice?

4) The screws did not come out easily. Normally I would put some WD-40 on the threads to put them back in. I'm thinking that it's flammable and not a good idea. What do you suggest? Thanks so much.

Freon
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- Furnace only "clicks", won't start

Post by Freon » Fri Feb 13, 2015 1:25 pm

Possibly you can clean the electrode without full disassemble. Try and locate the electrode. It should be about 1/8" in diameter and protruding from a white ceramic insulator. Using an emery board, you can try to clean it carefully. Google Honeywell Q348U1009 for a picture of an intermittent pilot assembly that clearly shows the ceramic insulator and electrode.

Having the power shut off to the furnace is all you need to remove the pilot assembly.

To remove the assembly disconnect the gas tube from the main gas valve. It's usually a compression fitting. If you can take pictures, I'd have a better idea. I am just guessing now. If it's a compression fitting you can simply reattach, carefully tightening the compression nut. Use any soapy spray, like 409, on the connection to see if there are gas leaks. You'll see the bubbles.

A drop of WD40 wont hurt but won't help in the long run.

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