Furnace Problems

[jlinder]

Having furnace problems and hope someone can help.

I have a 25 year old Carrier gas furnace (model 58SSL905) that will not light. The spark lights the pilot, but after about 20 seconds the main burner has not lit and the pilot goes out.

Some observations:
1. The sensor for the pilot light meters good. The spark keeps trying for about 3-4 seconds until the sensor gets hot enough.
2. After about 10 seconds there is a little flame from one of the burner gas ports. This and the pilot goes out after about 20 seconds.
3. Yes, the gas valve is turned on. Tried it also.(off and on).

I am wondering if what is happening is that the pilot lights, the sensor heats up enough to stop the sparker, then the main gas turns on but only enough to give the only little flame. After about 20 seconds the system decides the main burner did not light so it shuts everything down.

Of course that is just a guess.

Big question - where do I start looking for the problem? Any ideas?

 

[Bifflefan]

Re: Furnace Problems

Not that I know much about them but, Do you have a different thermostat to try?
If no, they are reasonably cheap for an electronic programmable one. Id try that first, I beat my head on the wall for a couple days once that heater guy came out and told me that was the issue.
Mind did about the same thing, the fan came on, the igniter snapped and then it shut down.

 

[KRS]

Re: Furnace Problems

Clean the ports (that's the wrong word for it) where the flame shoots through; we had a similar problem and once the long & skinny brush cleaned out the ports, the gas didn't develop turbulence from dust bunnies and it lit.

It's a cheap thing to try.

Not sure if the gas nipples are serviceable or not, maybe need to be cleaned (rust in the gas line).

KRS

 

[bruceb58]

Re: Furnace Problems

Sounds like a bad thermocouple. The control unit lights the pilot flame and then turns it off thinking that the flame didn't actually light.

I am assuming that when you said the sensor meters good, that you meant the thermocouple. I would still suspect it though. Its either that or the unit that the thermocouple goes to. The thermocouple is the cheaper of the two so if you wanted to throw a part at it, that would be the one to throw!

edit: re read your post and I see that your pilot goes on but the main burner is the one that doesn't stay lit. Is there a thermocouple for the main burnera well as the pilot?

 

[Eric 3.7LX Alpha 1]

Re: Furnace Problems

Your gas valve is going to require 24-volts to open the solenoid within it to open the gas. If you have a DMM, you can check it at the terminals on it for 24-volts AC, which should be after the pilot is lit by the ignitor.

There is the ignitor, pilot assembly and a flame sensor that the pilot flame should be either near or on. You can try:

Shut off the power to the furnace,
remove the flame sensor, usually 1-or 2 screws holding it in place,
Sand the tip of the flame sensor which would be in contact with the heat. maybe around 120 grit paper.
Reinstall it and see if it works.

Be careful the ignitor is very delicate and can be damaged if it gets bumped.

That flame sensor confirms the pilot has been lit before a bunch of gas is dumped in there. It gives the ignitor so long to do the job then it will eventually go into lockout.

See if there is a manual near the furnace. There will be a parts list and possible troubleshooting in there. Or you could also search for a manual online on the manufactures site.

Some of the newer furnaces have an led light inside on the circuit board which blink so many times to tell you a certain code and help troubleshoot it.

 

[dwco5051]

Re: Furnace Problems

Another possibility is a bad pressure regulator valve on the gas line. It allows enough gas to pass through to keep the pilot lit but after proving the pilot is lit and the main gas valve opens the pressure drops to the point that everything drops out due to low gas pressure. If the pressure regulator is vented to the outside check to make sure the vent line is open. Wasps don't just clog the telltales on outboards

 

[perchin]

Re: Furnace Problems

before you bang your head any further against the wall or spend a penny..... clear out the fresh air intake PVC and also the output vent PVC pipes.... seems from your description to be the culprits.

 

[jeeperman]

Re: Furnace Problems

Big question - where do I start looking for the problem? Any ideas?

Check and see if your propane tank is empty!
Or that a manual valve downstream of the tank is turned almost off.

In my younger years we had fun turning the main gas valve downstream of the natural gas meter off at the local McDonalds at about 2a.m.
P.O.'d alot of people when all those "managers" could not serve anything until about lunch time.

 

[18WCmerc]

Re: Furnace Problems

clean flame sensor with emery cloth or dollar bill, try that, then try a new thermostat

same thing happened to mine last year....

 

[windsors03cobra]

Re: Furnace Problems

Last one I fixed like that was a redundant and bad pressure regulator before the unit

 

[cpubud]

Re: Furnace Problems

sounds like a bad 740a pilotb assembly. pull the pilot assembly and clean the orifice it will work for a while but will need replaced its a 3 wire pilot assembly right?

 

[j_martin]

Re: Furnace Problems

In my younger years we had fun turning the main gas valve downstream of the natural gas meter off at the local McDonalds at about 2a.m.
P.O.'d alot of people when all those "managers" could not serve anything until about lunch time.

Some years back, the A&W drive in burned to the ground. Coupla kids decided to turn off the gas. Young, stoopid manager went out and turned it on right away. Relight explosion set the fryers on fire. It got into the greasy vents and could not be controlled.

 

[jlinder]

Re: Furnace Problems

Thanks for all the replies. Let me try to answer them.

1. It is fed by natural gas, not propane, so it is not a tank problem.
2. I have a gas water heater that has no problem, so it is doubtful there is a problem with the main gas feed.
3. Removed and tested the pilot light and sensor. It has 2 switches, One turns off the pilot igniter once it gets a little hot then the second closes once it gets a little hotter to turn on the main burners. Both sets of contacts test out good.
4. I cannot find the manual. I have looked on the web but no luck. The Carrier web site does not list the model (55SSL).
5. I will check on the voltage to the main valve relay, if I can figure out which terminals control the main valve. (Anyone have a hint). I guess 24VAC is pretty much a standard.
6. I will look into the possibility of the main jets being clogged.

Would it help if I shot some video and uploaded to Youtube for everyone to see?

Again, thanks in advance.

 

[jlinder]

Re: Furnace Problems

sounds like a bad 740a pilotb assembly. pull the pilot assembly and clean the orifice it will work for a while but will need replaced its a 3 wire pilot assembly right?

CPUBUD - sorry, I missed answering your response. It is a 3 wire assembly, but the pilot lights fine. The switches also check out good when the pilot light lights.

 

[perchin]

Re: Furnace Problems

again..... all the replacement parts in the world will be futile, if the intake and vent are not 100% clear. The furnace will not fully light and/or stay lit like its doing if its not venting properly.... I just had to run a fish tape through my mothers vent pipes. I pulled out a birds nest from the vent.... I also had the same problem in our first house.... went to light for the first time of the year and wouldn't fully lite..... found a dead bird in the fresh air intake.

I now make sure there are screens hose clamped on both the fresh air intake and vent pipes outside..

 

[dolluper]

Re: Furnace Problems

Your manual is here PDF file
http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/58ss-1si.pdf

 

[j_martin]

Re: Furnace Problems

again..... all the replacement parts in the world will be futile, if the intake and vent are not 100% clear. The furnace will not fully light and/or stay lit like its doing if its not venting properly.... I just had to run a fish tape through my mothers vent pipes. I pulled out a birds nest from the vent.... I also had the same problem in our first house.... went to light for the first time of the year and wouldn't fully lite..... found a dead bird in the fresh air intake.

I now make sure there are screens hose clamped on both the fresh air intake and vent pipes outside..

When cold hit last year, the furnace a the church wouldn't light. One or more of the church rug-rats decided that the vent pipe needed filling with landscape rock. We had to saw out a section to get at it all.

New vent has a screen on it.

 

[dolluper]

Re: Furnace Problems

Me thinks its the delay relay

 

[perchin]

Re: Furnace Problems

Me thinks its the delay relay

It could be..... everyone here has had good input.... it could be a lot of different things.... me just thinks it would be silly to spend money replacing parts, before one looks at the free fix, and likely culprit...

 

[dolluper]

Re: Furnace Problems

They can be tricky....esp when you have to have the door on for them to run....I use a snap clamp on the door switch....at least with the manual he can test the relay or set it or clean it before replacement