HVAC folks? Furnace won't kick in - thermostat clicks?

[Art Mulder]

When you said in your first post the pilot wouldn't light, was it the pilot or the main burner??

Pilot.

The way the thing normally works, is that the thermostat will give a click, and the yellow "system" LED will light. This causes the furnace to light, and 10-30 seconds later you hear the muffled "whump" as the main burner kicks in. Then another 30-60 seconds(?) after that the fan kicks in.

(I know, you know all this... )

With my problem yesterday evening, the thermostat would give the initial click, but then immediately give another click, so what I'd hear would be "click-click". The display would blink at the same time, and then nothing would happen for about 20-30 seconds and then it would try again. (so the system light did NOT light up.)

thanks again, Al.

[Larry James]

Art, hope you have it working - if not, here is some additional information.

This looks like a White-Rogers gas valve and ignition system - often called pilot-relight when used with a thermocouple. You have a version designed for induced draft furnaces.

The basic generic sequence is ...

1- Thermostat calls for heat, circuit between R (24 hot) and W (switched 24) energizes a relay and the relay (large silver box with terminals) starts the vent blower motor. Power may also be switched to the spark ignitor at this time, but gas is not yet following. Note: the gas valve does not have a pilot position, only on and off for this system.

2-When the vent motor up to speed and the combustion air switch ( the round control mounted to the right of blower in your picture) senses that combustion air is flowing and closes a switch proving air flow before the gas valve is allowed to open. Note: this switch may have 2 or 3 terminals. Also, the system may have a time delay to allow blower to purge combustion chamber before ignition.

3- After air flow is proven, the spark will light the pilot burner and the mercury sensor will heat up. The black control on the end of the sensing tube is plugged into the gas valve, as Al mentioned. This control usually (?) has a single pole double throw switch (SPDT) inside - like the switching action of a 3-way light switch that you likely have in your house.

4-When the sensor has heated up, proving there is a pilot flame available, the main gas valve is energized by the sensor switch. The pilot should light should ignite the main burners.

5-After a delay that allows the heat exchanger to warm up the blower should circulate warm air. Note: The blower may have a time delay as well as a bimetal sensor - the blower may turn on in this system even if the burner is off.

Al noted, "Looks like they're running the W on the thermostat to the Y on the furnace...haven't a clue why, sorry. Y is usually used for A/C, wondering if they use it to energize a relay or something?" This could be related to what is called a holding circuit that holds the pilot on after the mercury switch changes position (or not). EDIT: more on yellow wire-this setup may be used to supply 24 volts to the thermostat in the off cycle.


There were many variations to this system. That's why I called it "generic." I haven't repaired furnaces for over 25 years, but I repaired many systems with the mercury sensor. The most common problem was with the sensor, or quoting Al again, "...more common, is the pilot gets a bit dirty and won't always heat the cap tube hot enough."

I also give information under the:
"Art Mulder, hereby indemnify" clause. And how about this: "I, Art Mulder, hereby indemnify Larry James from any responsibility. If I do anything, I accept responsibility for my own actions." Whearas and so forth and the party of the first part and habeus furnace-us...

Best to find a "old timer" to repair the system, cause like I used to tell customers - "I can't fix them over the phone."

Let us know what the problem was when you have it working.

Keep warm, Larry

[Al Willits]

Art, you ever get the furnace looked at??
Just wondering how it went.

Al

[Art Mulder]

Art, you ever get the furnace looked at??
Just wondering how it went.

Al

Not yet... got a salesman coming by tomorrow to scare me with a quote on a new one. After that we'll probably go running back to our corners...

[Rich Konopka]

I had somethig similar happen with my Thermostat clicking and cicking and the Furnace false starting. I was he thermostat. I had a fancy digital programmable Robert Shaw Two zone switch. Replaced the battery and tightened the connections and it has been fine. Have you double checked the thermostat?

[Art Mulder]

Finally this morning I got the time to see about blowing out the pilot line. The furnace seemed to work for about 2 days at a stretch, then the click-click-nothing would happend and we'd have to reset it again.

So I disconnected it and blew it out.
pilot-end.jpg

Then I put it back together, and then the furnace wouldn't ignite the pilot. The exhaust fan would start, but that was all. I checked the flue outside and it was not obstructed.

This was odd, I hadn't touched anything but the pilot line and the igniter wire. I wondered if I'd jostled the wire loose, as it did have two cracks in it.

Called a few places, but neither one had the pilot relite part (it is a white-rogers). THe one guy told me that this is an old no-longer-made furnace and he would have to wait until monday to call his supplier to see if he could get a part. Even if I called a furnace repair guy, that guy probably wouldn't have the part either. Argh!

So I went back down and disassembled it again. This time I found a possible loose wire on one of the vacuum sensors. (this is connected to what looks like a temperature probe above the opening to the pilot area. Not sure what that would be for) I tightened that, and also had a look at the ignitor wire end. I wondered if I could cut out the cracked part and resolder it to the end. Can't do it though, as the connection is embedded in a ceramic shield.

But I put it back together and now the furnace sparks. I can hear it clicking. But now the pilot STILL won't light. ARGH! What could I have done?

I dunno what now. I just wanted to write, in case anyone had a brilliant idea.

...art

ps: FYI for any Canadians out there... I had a furnace quote: just a touch under $6000 for a new furnace. 60,000 BTU Armstrong (made by Lennox) with DC variable speed motor, and dual fire, (that is installed, with humidifier, taxes in, NO a/c). $600 less for no variable speed, and another $600 less for no dual-fire. (where's the fainting icon?) Better get a few more quotes...

[Al Willits]

Make sure the sparking is at the pilot and not to somewhere else, with the cracked insulator it could be arcing to chassis before it gets to the spark rod.
6k sounds a bit high, I think I'd get that second bid too..
Can you hear if gas is coming out of the pilot?
If so, I'd think that the spark is not at the rod or strong enough to light the pilot, maybe.

Al

[Art Mulder]

The guys are right now replacing my furnace.

And BOY am I glad we made that decision, because this is the heat exchanger in that old unit.
exchangerholes3.jpgexchangerholes2.jpgexchangerholes1.jpg

With all those holes we are really puzzled as to why our CO2 detector was NOT sounding.

These are all way at the top also, which would have made detection pretty tricky as well.

I'm going to sleep a lot better tonight.
...art

[Ken Fitzgerald]

Art...........There's little that I don't fix at home. I install and fix MR scanners, CT scanners, x-ray equipments for a living. In the Navy I installed and maintained all the equipments used in air traffic control centers...and equipments aboard nuclear powered subs..........I had a house burn down due to a gas leak when I was 6 years old. I don't ....I DON'T do anything related to natural gas....water heater...I'll relight the pilot.....furnace...I'll turn off power ....wait a while...turn it back on....That doesn't do it......I call the PROS! I do my own plumbing, carpentry, electrical........I don't do gas....... except for the gases (helium) used in the cryogen systems of supercooled magnets used with MR scanners......

[Al Willits]

Popular misconception that all furnaces with holes in the chamber produce CO, not true.
That's why your CO detector didn't register, assuming it was working correctly.
Most manufactures recommend a yearly inspection of their furnaces, and it is a good idea.

Good thing they found the bad chambers though, when the exhaust gases go back into the house and get burned again, you will/can start to get CO, or if the holes get big enough to cause flame distortion that will/can cause CO.

Al

[Art Mulder]

Hey Al, one last thing...


The guys ripping out the furnace also discovered that the condensate drain line was plugged somehow. This meant that it wasn't draining properly, and the exhaust blower was sitting in water, and probably not generating enough suction.

Yet the technician we had out on Saturday completely missed that. I can't really blame him either. Who would check that?

[Al Willits]

Loaded question, but you'd think the first guy would have caught it, did the furnace run for the first guy?
If so, that could be why he missed it.
If it didn't, I'd say he missed the boat here, remember I wasn't there and asking second opinions over the iner net is chancy.

I will say plugged condensate lines are/can be common, and should be checked from time to time.
If the furnace didn't come on because the combustion air motor was running to slow, jumpering the pressure switch out would have probably shown that, least wises the probalem was in that circuit.

One of the basic checks for a chamber having holes or cracks in it, is to run just the blower (house air, not combustion blower) and not the burner, then stick a match into the chamber, if you see flame distrortion, good chance a chamber is bad...not in concrete, but a good indication.

Good part is that you are now headed for a new furnace and safe.

Al