Little bungalow in US midwest. Heil gas furnace on it's 2nd season.
Standard forced air, std install. Gen'lly works well.

Heat cycle begins:

1.) t-stat calls for heat
2.) Inducer fan spins and pressure switch closes (15+ sec)
3.) Igniter is powered (17 sec)
4.) Gas valve opens, burners fire. Flame senser keeps gas valve open when heated.
5.) Igniter is powers down
6.) Blower runs after 30 sec

Works OK about 4 of 5 times.

The fifth time, it works OK thru 3.). The igniter is like a glow-
plug: I can see it red-hot. The gas valve opens, and the burners
fail to fire. It then flashes the code for burner-fire-failure, and
goes back to 3.). It usually (but not always) works on the first re-
try.

There is a lockout after 3 failed tries. This hasn't happened yet.
It's a good thing: it's damned cold here.

Inside of the unit looks clean as a whistle. I blew compressed air
thru the lead burner anyway. I've inspected the igniter and flame
senser. They look fine. The contractor's roving trouble-shooter
suggested goosing the (gas) manifold pressure, which I've done. No
apparent help.

Not certain where to go from here. Any/all info/suggestions etc much
appreciated.

Cheers,
Puddin'

 

if it is only 2 years old call the original installer out.
It should be under warranty. and the service call won't cost you a dime. If you attempt to fix this you will void the warranty

 

I guess I should've run the whole thing down so as to avoid the easiest and least relevant response. Apologies: I figgered it was implied.

Got a good late-season deal on install in Mar. '06. 2-year warranty expired Mar. '08.

P

 

I was talking more about the manufacturers warranty.
do you have your furnace serviced yearly?

 

Huh??? manufacturers warranty is parts-only, 5 yrs.

Not if it doesn't need it in the first few years.

Not at all certain why you are asking ... do you often respond without addressing the posted problem?

P

 

Your ignitor shoud be glowing actualy quite a bright yellow, that is so bright you can barely look at it. You may want to ohms test it. Also make sure that how it is mounted that the mount looks square so it is oriented where it should be close to the burner.

Test pressure switch - as something may be going on where it is always on the cusp of not working, and is borderline due to something a little off in the drafting. Could be something as simple as ice at an intake or exhaust PVC pipe outside.

Today, I had a 5 minute diagnosis on boiler outage, and first thing I checked was the pressure switch and found outgoing 24 volt wire dead with inducer running. I alligator clip jumper wired across the two terminals and it fired right up. So then I went outside and found plastic grocery bag sucked partially into intake pipe!

Test voltage coming to gas valve to make sure it is getting there.

IF - a big if - no problems like I mentioned, then rap on the gas valve, when it should be igniting, with butt end of screwdriver and see if the flame comes on.

 

As I mentioned, it has been inspected. It looks 100% OK. And it works OK 80% of the time.

Did you read the post? If the pressure switch didn't close, the igniter wouldn't energize. The pressure switch is 100% A-OK and F-I-N-E.

The bags fly around like crazy here when the wind blows.

Did you read the post? I *always* hear the gas valve actuating.

You mean tape (or whatever) the safety switch so I can run thru cycles with the front covers off?

The gas valve *always* makes the distinctive sound when it's supposed to. Sounds the same when the burners fire as when they don't.

P

 

Apologies for not mentioning ... it is a simple 1-stage Heil furnace in perhaps the simplest imaginable application. Absolutely nothing of a complex or complicating nature.

P

 

I guess I said a lot of wrong info in my last post. I fly around this board here awfyully fast trying to help everyone. Certainly bound to slip up once in a while.

So the bottom line is you basically are hearing the gas. But nothing fires up.

You do realize right?, that even though one of those HSI glow coils glows, it is possible it does not quite glow QUITE bright enough, and will not fire up the gas? Just so you are aware of that. This has fooled many people as they see it glowing pretty bright, and think there is no way it can be that glow coil. Yet it is. Been there done that. Actual experience, not theory.

That is why I said about actually ohms testing it. It should be somewheres under 100.

Do you have a gas meter where you can go out there and see if the 1/4 or 1/2 foot dial moves when the gas valve opens? That actually should be your first inspection before even checking out the ignitor. THEN you will know which direction this investigation needs to be heading. Such as test HSI. Such as shut off the inline gas valve by furnace, disconnect gas line downstream of it, and smell for actual gas, and maybe allow some pressure regulator vent to reset itself after rehooking up and turning gas back on. Rapping on the gas valve. Stuff like that. I've gotten some furnaces going that gave me EXACT symptom as you, in such a mannor. On one, the gas did not even smell like gas when I disconnected the gas line and ran it a couple of seconds disconnected! Then after I rehooked it up, it fired up.

 

I've stood over the unit and observed the cycle many times. The gas valve *always* clicks (*always* actuates). 80% of times the burners fire. 20% of the time they don't.

"Igniter should measure between 40-70 OHMS at room temperature."

The igniter measures 45 ohms.

I supposed that the igniter could be borderline hot enough to exhibit the intermittent behavior, but the tech didn't seem to think that to be likely. It was worth measuring.

The tech said a regulator external to the furnace could result in low gas pressure. I checked the line: there is no such regulator.

I give up. What was the cause of the problem? Funny regulator??

I just look for stuff that could be a point of failure. The gas feed (meter, lines, etc) look fine, and have always worked OK. I'm not gonna disassemble everything. Contractors bill per call + time. Totally different for me.

The mystery persists ...

P

 

My guess is the problem lies with the gas valve. The click does not mean the valve actually opened. It only means the solenoid was energized. You could use a BBQ lighter near another burner & away from the hot surface ignitor to test if the ignitor was not getting hot enough. If the burner lights with the flame but not the HSI, that would certainly tell you it's an HSI problem.

 

Check.

The problem seems to be more infrequent sinceI goosed the manifold pressure a bit more. Makes it trickier to test.

Suppose I up the set-point temp 5 degrees or so, go down the basement and shut it down with the main 120v switch time-and-again until I can get it to fail and test with the BBQ lighter. Would it hurt anything to test in such manner?

What does H-S-I stand for?

Thanks,
P

 

Sorry, HSI stands for Hot Surface Ignitor (or Ignition). I'm sure you don't have one but a manometer is the easy way to check for gas thru the gas valve. A manometer is easy to make & if I can find the link to how to do so, I'll post it.

For testing purposes, disconnect the thermostat leads from the furnace & use a jumper wire between R & W. Turning the furnace on & off with the switch often will mask a problem.

 

I found the link on how to make a U-tube manometer.
RV U Tube Manometer

If you are using natural gas, the pressure will be a lot lower (around 3.5 - 4.5"). The one change you will need to make to the design is to install a barbed x 1/8" male pipe thread adaptor in the end of the hose the drawing shows hooked to the burner. This male pipe thread will screw into the test port of the gas valve.

 

Thanks. I haven't noticed the problem lately ... maybe it'll just "go away" ... (hope, hope). :-)

It's a simple 4-wire tstat. If I pull the 4 and jump Red and White and it fires the burners per spec, what do I do to further test? Disconnect/reconnect the jumper?

Thx,
P

 

The jumper serves as the thermostat. Removal shuts the burner down & installation will fire the burner just as if it were the thermostat callling & being satisfied. It's a whole lot easier to jump at the furnace rather than running up & down stairs.

 

Test port? All I see is an inlet port and an outlet port on the diagram. Didn't *notice* one on the valve, either.

A Great Idea.

Simply doesn't work for me. Draft from the idiot inducer extinguishes my BBQ liter.

Thanks,
P

 

This test port should be plugged with a 3/16" allen head plug.

 

Apparent problem resolution.

I got some help. Somebody with equipment.

Pressure in/out of gas valve was fine.

No *apparant* problem with igniter, but ...

It mounted on like a thin sheet-metal shelf that appeared to have warped a bit with the temp changes.

We bent the shelf back, accidently broke the igniter, installed a new one. Furnace now seems OK.

Much thanks to Grady.

Cheers,
Puddin'

 

It sounds like your equipment uses the HSI as a flame sensor as well as the ignitor. Those ignitors are pretty fragile. I don't know how much help I was but Thank You. Glad you got 'er fixed.