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dm19891

join:2004-07-03
Columbus, OH
kudos:1

Furnace starts, then shuts off.

Rheem Criterion model.

It begins its power-on cycle normally. First the updraft blower turns on for a bit, then the HSI glows bright orange, then the gas turns on and the flames ignite fully and the big blower turns on.
About 3 seconds after the gas ignites, it shuts off. That is the gas shuts off, the blower continues for about a minute then it shuts off. This cycle will repeat a few times, then usually after the second or third time everything stays on and works normally.

Is there some kind of flame sensor I can check/clean/replace?
Anything else?

Would any pics be of help?

Last work done was the HSI was replaced two years ago.

robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1
How long is it after the big blower cuts on that the gas shuts off?

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel

4 edits
reply to dm19891
My guess would be that the pressure switch is opening.

It may not necessarily be faulty, there could be an underlying cause. When the blower kicks on, it's pulling vacuum or putting pressure where there shouldn't be, causing the pressure switch to open.

You could very easily determine if this is the cause if you have a multimeter. Set it on to measure AC volts, and connect it across the pressure switch. Turn the furnace on, once the inducer blower is running you should read 0 volts (switch is closed). You should continue to get a closed 0 volt reading throughout furnace operation. If you read something different (such as 24V open) when the problem occurs, then you know that's what it is. Next step would be firguring out why the switch is opening, but that would be best left for a professional to figure out.


cowspotter

join:2000-09-11
Ashburn, VA
kudos:2

1 recommendation

I'm gonna say flame sensor. Look at the burner furthest away from the ignitor. My furnace has 3 burners, ignitor on the far right, and the far left has the flame sensor. It's a probe that sticks down into the flame path to sense that the burners all ignited properly.

You can remove it and clean it with some emery cloth. That should bring it back into operating condition to test. If that works you may want to consider replacing it.


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK

1 edit
reply to dm19891
Click for full size
Click for full size
Yeah I'd suspect your Flame sensor too. It's maybe dirty, or failed.

I have a similar Furnace. (Rheem Criterion II)

Here's the pics:

Basically, you can unscrew it, pull it out, and clean it off with some steel wool (edited to reflect Sandshark's advice) etc. I watched the service guy do this to mine on the annual checkup. Mine's shiny and clean. (Sorry about the crap picture, camera one hand, flashlight in other, etc)

Check yours, see if it's got oxidization/carbon buildup etc
--
"Fascism should more properly be called corporatism because it is the merger of state and corporate power." -- Benito Mussolini

PrntRhd
Premium
join:2004-11-03
Fairfield, CA
reply to dm19891
Another thing that causes similar issues is a clogged intake air filter.

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel
reply to KrK
said by KrK:

Yeah I'd suspect your Flame sensor too. It's maybe dirty, or failed.
He did say that the burner actually ignites and stays on though, and then kicks out 3 seconds after the main blower comes on.


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK
said by TheMG:

said by KrK:

Yeah I'd suspect your Flame sensor too. It's maybe dirty, or failed.
He did say that the burner actually ignites and stays on though, and then kicks out 3 seconds after the main blower comes on.
The way I read it the blower comes on, the igniter ignites the gas, and three seconds later the gas shuts down, killing the burners, and then the blower finishes the cycle.

That's exactly what mine does if the flame sensor is disconnected. The guy checked the safety on the inspection by firing it up with the flame sensor d/c'ed. The thing fires, the flame sensor doesn't detect it, safety kicks in and shuts off gas.
--
"Fascism should more properly be called corporatism because it is the merger of state and corporate power." -- Benito Mussolini


CylonRed
Premium,MVM
join:2000-07-06
Bloom County

2 edits
reply to TheMG
said by KrK:

said by TheMG:

said by KrK:

Yeah I'd suspect your Flame sensor too. It's maybe dirty, or failed.
He did say that the burner actually ignites and stays on though, and then kicks out 3 seconds after the main blower comes on.
The way I read it the blower comes on, the igniter ignites the gas, and three seconds later the gas shuts down, killing the burners, and then the blower finishes the cycle.

That's exactly what mine does if the flame sensor is disconnected. The guy checked the safety on the inspection by firing it up with the flame sensor d/c'ed. The thing fires, the flame sensor doesn't detect it, safety kicks in and shuts off gas.
Pretty much exactly what happens when our flame sensor needs to be cleaned as well.


SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3
reply to dm19891
A poor flame sensor current will show by the yellow flame sense LED light on the circuit board located in the blower compartment. If flame sense current is good, the light will be steady. If flame sense current is poor, the light will flash. You will have to check this with the blower door off (since there is no site glass) and by manually engaging the door safety switch. Just be careful when doing this and be sure nothing can get sucked into the blower when it starts. If the flame sense LED shows the current is poor, turn off the power to the furnace, remove the flame sensor, clean with steel wool (not emory cloth/sandpaper), install and check.


hambone42
Peace, through superior firepower
Premium
join:2002-02-02
Manassas, VA
Reviews:
·Comcast
reply to PrntRhd
said by PrntRhd:

Another thing that causes similar issues is a clogged intake air filter.
+1 to this one. I found a "hidden" filter I didn't know I had that was almost completely blocked, and causing the pressure sensors to shut down the burners a few seconds after the main blower came on.
--
Sarcasm is the Body's Natural Defense Against Stupidity

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel
reply to dm19891
Hmmm the OP is a bit unclear now that I read the post again.

He mentions that the main blower comes on, and also mentions that the gas cuts out 3 seconds after igniting.

That doesn't make sense, as normally the main blower does not come on until later in the sequence, after the burners have had a chance to warm up the heat exchanger.

Unless this particular furnace is designed a bit differently than most or something.

Anyways, one thing that should be mentioned is that the diagnostic LEDs on the controller board should indicate the fault condition. So I guess it's time for the OP to dig out the instruction manual and have a peek at the LED code.


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK

2 edits
Ok you got me curious, so I went out and observed a start up. Mine is a Criterion II.

The thermostat calls for heat, then a blower starts up. But it's not the blower that blows air into the house? Or maybe it spins at a slow speed or in reverse or something... I'm not sure but it's definitely some type of blowing/venting BUT is not coming into the house yet.

Then the igniter starts firing and about 1 sec later the burners ignite. Then the burners burn for maybe 10 seconds or so and then the air starts coming out through the house vents. This seems designed so it doesn't fire a few seconds of cold air into your house first.

The only way to learn more would be to take the doors off and watch it again (with the safety interlock pressed).

--
"Fascism should more properly be called corporatism because it is the merger of state and corporate power." -- Benito Mussolini


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2
reply to dm19891
I would vote for the flame sensor as well. At least it is worth a look. I have a Carrier gas furnace, but it looks very similar to what KrK posted, and I have to clean the sensor every other year or so. Same symptom. A quick cleaning with some fine steel wool fixes it for another two years.

Question: Do you have a small window in the lower panel through which you can see a red LED. When my sensor acts up, it will cause the LED to flash a code (the cryptic deciphering messages that correspond to the flashes are printed on a sheet on the inside of the lower front panel).

On mine, if it fails three consecutive times, it will go into lock-out for three hours. In the dead of winter, it can get mighty cold in three hours; that is usually when I discover that it needs to be cleaned.

One word of caution. Be sure to secure power to the furnace if you decide to try and pull out the sensor to clean it.
--
Shine on you crazy diamond...


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2

1 recommendation

reply to KrK
said by KrK:

The thermostat calls for heat, then a blower starts up. But it's not the blower that blows air into the house?
What you hear is a small draft motor towards the top of the furnace that promotes venting and fresh air in the ignition spaces during start-up.
--
Shine on you crazy diamond...


bulldog6769

@sbcglobal.net
reply to dm19891
It wouldn't hurt to clean the flame sensor, you may want to take a look at the over-temp limit switch (assuming this furnace has one) it is probably located above the burner area, on the housing that the blower blows air across before it is circulated into the house. Incidentally is your flame color orange or blue? It should be blue.


Vchat20
Landing is the REAL challenge
Premium
join:2003-09-16
Columbus, OH
reply to KrK
said by KrK:

The thermostat calls for heat, then a blower starts up. But it's not the blower that blows air into the house? Or maybe it spins at a slow speed or in reverse or something... I'm not sure but it's definitely some type of blowing/venting BUT is not coming into the house yet.
If it is anything like the furnace in our house (Most operate in fairly similar fashions as far as procedural steps to normal operation), that would be the blower that pulls in combustion air for the gas.

Essentially it should operate like this:
1) As the thermostat calls for heat, the furance kicks on the combustion air intake blower.
2) After a given period that #1 runs, the gas valve opens and the burners ignite (obviously sometime around here the igniter lights to accomplish this)
3) After the burners run for a sufficient period to heat up the heat exchanger, the main forced air blower kicks in.
-Now during this period the intake blower will continue to run as long as the burners are lit-
4) After the thermostat is satisfied and ends the call for heat, the gas valve shuts, burners go out, and the intake blower cuts out.
5) After a sufficient amount of time for the heat exchanger to cool down (some furnaces use a temp sensor, others go by a set time delay. Mine is the latter and the delay can be set via jumper on the control board), the main forced air blower shuts off and that is that until the next time a call for heat is made.

To the OP, I will concurs with the others here on the flame sensor. That seems to be the most common culprit of all especially of the furnace has not had a checkup or maintenance in a while. And it is the easiest and cheapest to check. Take it out and clean it yourself. If that does not solve it, then you can go down the next options until something sticks.
--
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz

8744675

join:2000-10-10
Decatur, GA
reply to dm19891
If your furnace is fast cycling like that, check your thermostat. Mine was first running for very short cycles on and off but long enough to heat up the house. I thought it was the way a new furnace worked (there used to be a pulse furnace that came on and off in short cycles). Then it got worse until it would cut back off almost as soon as the gas came on, then it wouldn't even get that far and I had no heat.

Of course, the furnace lit up on the first try when the service man came the next morning, but he noticed it was cycling on and off too fast and checked the thermostat and that was the problem. I didn't replace my old Robertshaw mercury switch thermostat when I got the new furnace.

It turned out that the heat anticipator on the thermostat failed and was telling the furnace that there was almost enough heat in the house way too soon until finally started cutting off the furnace before it even cycled all the way on.

It cost $20 to replace the thermostat myself, but $90 for the service call, which was worth it because I would have never guessed it to be the thermostat.

retired17
Premium
join:2007-01-24
Anaheim, CA

1 recommendation

reply to dm19891
I had a furnace that had exactly the same symptoms. It turned out to be a defective air flow senser. That is the furnace checks that the blower is actually blowing by sensing air flow with a tempetature gauge. As long as the temperature measured relatively low, the blower was blowing. If not, it turned off the furnace. Checked that, too.


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK
reply to rockotman
said by rockotman:

said by KrK:

The thermostat calls for heat, then a blower starts up. But it's not the blower that blows air into the house?
What you hear is a small draft motor towards the top of the furnace that promotes venting and fresh air in the ignition spaces during start-up.
Thank you
--
"Fascism should more properly be called corporatism because it is the merger of state and corporate power." -- Benito Mussolini


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK
reply to retired17
Yeah, the overheat safety cutout. The guy checked that too on the maintenance check. He disconnected the blower motor while the furnace was running, simulating a failure. After a short period, the furnace shut itself down.
--
"Fascism should more properly be called corporatism because it is the merger of state and corporate power." -- Benito Mussolini

mc5w

join:2002-06-14
Independence, OH
reply to dm19891
I also had this problem with a furnace. Turns out that the wiring harness plug for the control board was wiggling loose causing all kinds of false control faults. It is a Molex type plug and there are two tabs that do not necessarily lock into place unless purposely squeezed into the locked position. I then used some 1/2 inch wide colored electrical tape and some rubber bands to assure that the tabs would stay locked into the socket.


dm19891

join:2004-07-03
Columbus, OH
kudos:1

2 recommendations

reply to dm19891
Click for full size
Well first off a little clarification: after the gas ignites, it takes about 10 seconds for the big blower to kick on. About that same time is when the gas shuts off.

After digesting a lot of good info from you folks I did this:

I turned up the thermostat to make furnace turn on, with the door cheated.

I observed the yellow "flame" LED--it never came on.

Then, I removed what I'm pretty sure must be the flame sensor. It looks pretty dirty, like "normal burnt dirty" So I cleaned it up with some steel wool and put it back in.

Turned furnace on, after flames ignited, the yellow "flame" LED lit right up. Flames stayed ignited!

Myth busted! --wait, wrong show...
Problem solved!

Thanks all.


rockotman
...Blown On The Steel Breeze
Emerging Research
join:2000-08-06
DSotM
kudos:2
said by About 100 posters in this thread :

Told ya!

--
Shine on you crazy diamond...


tsw1976

@kitusa.com
reply to dm19891
My furnace has four burners. only the two center ones will start up. as i was reading through the post I was thinking maybe mine was the heat sensor. but the two outside burners which the one has the heat sensor is not firing up. i have a switch on the side of my furnace for the power and if i turn it on and off 2 or three times then i can get all the burners to kick on. I assume that it is shutting down the gas but why am i not getting those two outside burners to kick on?

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel

1 edit
My guess would be inadequate gas flow or dirty orifices.

I assume the pilot in your furnace is located in the center of the 4 burners. The flame from the main burners is supposed to spread just enough to allow the remaining burners to ignite. If the burners are dirty or if gas flow isn't correct the burners not directly in contact with the pilot will fail to light, or experience delayed ignition (not a good thing).

This problem IMO is to be left to the pros. A furnace that is not igniting properly can be dangerous (unburnt gas from the non-ignited burners can explode).


Anon User

@swbell.net

1 recommendation

reply to dm19891
Don't want to register but wanted to reply. This thread described the very same issue that I had. Turns out that cleaning the flame sensor did the trick. VERY simple to do and can help you avoid high repair costs. Took me all of 5 minutes to do. Thanks guys!!


tsw1976

@kitusa.com
reply to TheMG
Thank you. I contacted my heating and air guy and he did say it sounded like the holes were clogged not allowing the gas to flow to the two burners. I cleaned those out and it works great now.


Richds

@comcast.net
reply to dm19891
I just fixed my furnace by doing this. I had some diagnostic lights on the front and one did a slow blink at the end of the startup cycle, then shut off the main burner. I got a rough sponge and cleaned some carbon buildup off the flame sensor, then it started right up. Thanks for the tips! BTW I have a Rheem 90 horizontal unit.


KrK
Heavy Artillery For The Little Guy
Premium
join:2000-01-17
Tulsa, OK
reply to dm19891
Congrats, you fixed it yourself, your family now thinks you're some kind of HVAC wizard, and you saved a $75 service call.