Furnace not working correctly

2298 Views 24 Replies 5 Participants Last post by yuri, Jan 19, 2020

epeterson777

Discussion Starter · Jan 18, 2020

Hello, I have a Heil 7000 furnace that hasn’t been working right. Of course it is a weekend so I’d rather not call anyone to pay weekend rates. I have done some basic troubleshooting but does anyone know of a good website that has a systematic way to troubleshoot?

The induction fan comes on, flames will light, blower fan blows then blows, then after about 45 seconds the flames will go out and the blower will run for a minute or so. After the blower shuts off I can hear an electrical humm but can’t find where it is coming from. After about 5 minutes it’ll repeat the process.

There doesn’t appear to be a flame sensor that I can find on this model. The igniter is working fine, the induction blower is working fine (I did change this about about 2 weeks ago because the old one sounded like it was going to explode, so that could be related). I sucked on the pressure switch and checked for continuity and it worked, however there was a drop of water that came out when I disconnected the line from the induction fan housing. I blew the line out. Reconnected it and then the furnace ran for a couple of minutes so I wonder why that changed. After that first cycle it went back to the roughly 45 seconds of working.

I suspect something with the pressure switch but I don’t know. Is there a good troubleshooting chart somewhere to run through this?

Thanks

1 - 20 of 25 Posts

user_12345a

· #2 · Jan 18, 2020

Check voltage drop across the pressure switch when the heat is on and see if it drops out just before the burners do.

Does your furnace have a honeywell smart valve? Igniter plugged into the valve, hot surface pilot ignition?

If yes, post the number off the valve.

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yuri

· #3 · Jan 18, 2020

Post some pics of the furnace with both doors off.

There are dozens of versions and models of Heil furnaces out there.

Go Advanced> Manage attachments

epeterson777

Discussion Starter · #4 · Jan 18, 2020

I checked for voltage at the pressure switch earlier, and it seem to go at the exact same time as the burners went out. I didn’t notice it going outside it before. It does not have a Honeywell smart valve. It is pretty old. I think it’s 22 years old.

I will try to get some pictures with the lower panel off later. It started working again now so I don’t dare take the lower door off and trip the safety switch in case it starts to act up again.

I have a thermostat programmed to go down at night. This morning was the second time this week that it has acted up. It seems like it’s struggles to pick up in the morning when the demand is put back on it.

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roughneck

· #5 · Jan 18, 2020

What’s the model number? 7000 is just a model line.
Does that furnace have a diagnostic light?
Do you have a meter?

yuri

· #6 · Jan 18, 2020

Make a video of it when it starts up when cold and post it on You Tube and link it here.

There are no diagnostics for that unit and it is closer to 30+ yrs old. Has the original Honeywell S86 control with the combo pilot burner with electrode and flame sensor as one.

There are no flow charts for it that I have seen and I worked on hundreds of them. Most are obsolete where I am as the cost of repairs is too high. especially with that inducer blower.

Try find where the thermostat wires attach on a terminal strip in the blower compartment. Remove and label them. Then put a jumper between R and W and press the door switch in and see how long it runs.

If it keeps running then your thermostat/tstat is faulty.

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surferdude2

· #7 · Jan 18, 2020

Did you change the entire inducer assembly or just get an aftermarket motor and fan cage? If not complete assembly, verify the fan rotation matches that volute direction.

user_12345a

· #8 · Jan 18, 2020

Pretty simple controls setup to troubleshoot, much better than the smart valve - just use your meter.

pressure switch diagnostics would need a manometer.

post a clear pic of the schematic - it's on the blower access panel facing in in most cases.

epeterson777

Discussion Starter · #9 · Jan 18, 2020

3

I jumpered the W and R terminals and ruled out the thermostat. It is very intermittent now so I tried to get a video of the cold start to failure but of course then it ran normal.

When I changed the induction motor it was the whole assembly including the fan and housing.

I did catch this video earlier of an electrical spark that relates to it shutting down. You can see that spark, when that happens it shuts the flames and induction motor off and then the blower will run for a little while and then it shuts down.

I took some better pictures of the unit including the schematic. I do have a meter and I have a manometer at work. I just lack the basic understanding of how all the components relate and sequence with each other.

Rather than hire someone to fix this issue, I have decided I am going to limp it along until I can get a new furnace installed since it is so old and the burners look pretty rough. I have a gas fireplace that can maintain the temp in the house. Of course this crap happens when we aren’t supposed to get above 0 for the next couple of days so if I can find a fix to get me through a week or so until I can get a new one that would help.

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roughneck

· #10 · Jan 18, 2020

Is your fireplace ventless or vented?

surferdude2

· #11 · Jan 18, 2020 (Edited)

That looks like it might be the flue temperature limit switch arcing as it opens due to high temp but wait for yuri to verify, he'll know that location.

I think the flue temp switch is located down lower (maybe even on the blower housing) so that flash may be misleading. If it happened as the fan went off, it might have been the normal fan relay contacts flashing or the normal system relay contacts flashing.

Even so, the flue temp switch cutting out is still the prime suspect. Have you checked the flue for any obstructions? Might just be a bird nest or something. Ice and snow can also plug it.

Certainly fits the symptoms but so does other things.

user_12345a

· #12 · Jan 19, 2020 (Edited)

Did you change the inducer before or after this problem started?

Does the the inducer stay on when the burner drops out?

I believe the white box where it sparked is the system relay and it energizes the inducer and separately, the ignition module.

I can verify if you give me the data off that box.

You should check the connections.

The arching could indicate a bad connection - i would check.

Also very possible that there's an internal problem - connection or otherwise.

When there's a call for heat, the system relay gets energized.

One side of the relay passes power to the ventor power and the pressure switch closes

The other passes control voltage to the ignition module through the pressure switch.

The ignition module applies power to the pilot valve and powers the spark igniter. When a pilot flame is detected, it applies power to the main valve.

If flame is lost, it closes the pilot and main valve and goes through the ignition sequence again.

When the pressure switch opens up, power to the ignition module gets dropped and the inducer stays on.

The fan control detects when the valve is energized and starts a timer -> after the time delay, it applies power to the blower which passes through the normally closed parts of the fan relay and to the heating speed tap on the motor.

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epeterson777

Discussion Starter · #13 · Jan 19, 2020

I changed the inducer about 2-3 weeks ago and it was working fine until a couple of days ago. I still have the old one so I might put that in for troubleshooting purposes and if it works I can live with how noisy it is until I get a new furnace.

The furnace seems to be acting different now. It will all fire up like before but now everything (blowers and flames) is shutting off at the same time. Which seems odd to me since I figured the blower would keep running to cool things down but now it is shutting off as well.

I’ll check the flue for obstructions soon and report back.

epeterson777

Discussion Starter · #14 · Jan 19, 2020

Problem Solved!!

There is a bad connection or some issue with the white box where the spark was. I wiggled the wire bundle going to it and it sprung to life and kept running as normal. Due to the intermittent ness of this problem I’m going to monitor it for a while. All of the connections are tight so I’m assuming that terminal is probably loose or screwed up internally and me changing that inducer assy. and messing around in there must have moved the wire just enough to make the problem show up. I feel like an idiot for not wiggling playing with those wires sooner, however with the symptoms, I was thrown off.

Now that I am not going to be forced into buying a furnace immediately, I can do it this spring or summer when it isn’t subzero outside. With that being said, I am a very mechanical person and always prefer to do things myself, is installing a furnace something that a person with decent mechanical skill can tackle or are there too many code considerations to worry about? The thought of CO or gas issues does concern me. My thoughts are if I did it I would hire someone to come look it over and make sure everything is good. Thoughts?

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user_12345a

· #15 · Jan 19, 2020 (Edited)

I suggest fixing the connection - replacing the component if required.

The heat exchanger could be cracked and that should be checked asap - easy if you don't have a/c coil right above, can be inspected from the top.

Much harder otherwise.

Replacing a furnace is not close to diy friendly unless you really study up on the theory and am comfortable with sheet metal work, gas lines, etc. Proper sizing and commissioning are very important.

I really suck with sheet metal so I wouldn't go the diy route despite knowing the theory.

Older furnaces can be more reliable than the new ones, yours is already high efficiency so I wouldn't rush to replace unless something is wrong that's not worth fixing.

The new ones are made as cheap as possible and won't last 30 years. 20 if you're lucky!

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user_12345a

· #16 · Jan 19, 2020

on yours looks like u can remove the burner shield and inspect from the inlets - can't see the entire thing though.

surferdude2

· #17 · Jan 19, 2020

I liked the old stuff better... older than that one even. The big beefy components lasted longer and there was no circuit board to fail. You could have about all the parts you needed in the truck and fix things on the spot. Life was simpler for a repairman.

Just sayin'... I realize they're a lot safer and more efficient now. It takes more training, more test equipment, higher priced parts and a bigger truck now and often longer turn around times. All that adds up and the customer takes the hit.

user_12345a

· #18 · Jan 19, 2020

The manufacturers could standardize circuit boards (relative to type) if they wanted to - drop a chip in for the specific firmware.

They wouldn't be able to charge so much though!

yuri

· #19 · Jan 19, 2020

That white box looks like a Camstat fan timer. When the gas valve energizes from the S86 it powers up a fan timer to start it off time rather than the fan control which it uses later.

As far as I know Camstat parts are long obsolete. The burners on most of them rot out at the sides ( rust out ) and you get flames going sideways instead of vertical and then poor combstion.

I would buy a new furnace after Winter. The heat exchanger can crack at any time.

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surferdude2

· #20 · Jan 19, 2020

I got busy elsewhere so I'm a little late posting this picture that labels the components as best I can figure. I'll put it up in case it may still be of some use or may help some other poor soul with the same problem.
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