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-   -   Carrier won't stay lit (http://www.diychatroom.com/f17/carrier-wont-stay-lit-33242/)

kurto 12-05-2008 10:00 PM

Carrier won't stay lit
 
I have a Carrier 58RAV070-12 furnace that I could use some advice on. It is approx 11 yrs old. It is a central air furnace - natural gas supplied.

The main problem I'm having is it will not stay lit. When it calls for heat the burner lights up, then after a few seconds it tries to ignite the rest of the way (for lack of a better way to describe). Immediately it will click/shut off. This will repeat the lighting process 3 times before lock out. Then I have to push the two reset buttons to overcome the lockout.

At some point I did get quite a lot of smoke in the room but I was by the thermostat so I couln't really tell the direct source of it. However, I could not see anything that fried or anything. This happened in the middle of everything and the furnace did not act any different after this than it did before.

Now, I have gotten it to stay going for about 10 minutes until I turned down the thermostat to auto shut it off. The burner shuts off but the fan just keep going. I could only get it to stop by cutting the power to it. Then when I turn the power back on it stays off as expected.

If I set the fan to "on" at the thermostat it will run and shut off accordingly as expected.

Not sure if any of that is related to the reason why the burner won't keep going.

Any advice would be GREATLY appreciated!

Thanks

SKIP4661 12-05-2008 10:21 PM

When the burners light is the flame forceful or lazy. Could possibly be a gas pressure problem.

kurto 12-05-2008 10:31 PM

It is lazy at first - similar to a pilot coming on. It will really ignite, which you can really hear and tell for a few seconds before shutting back down to 'pilot status'.

How would I check for a gas pressure prob? Thanks

SKIP4661 12-05-2008 10:54 PM

If you have other gas appliances check them for proper operation also. If you have snow and ice it may have obstructed the vent on the gas regulator at your meter. The regulator may also have failed and should be checked by your gas supplier.

NYCtinman 12-06-2008 12:08 AM

Try if you can - the flue(chimney) for any blockage --

kurto 12-06-2008 11:19 AM

Water heater is gas and works fine. No snow or ice this season so that would not be an issue. I will check the flue but that is unlikely since it has the proper cap on top which would prevent anything but a bug from getting in. Thanks for the replies.

lrfllc 12-06-2008 02:37 PM

Furnace problem
 
When you say you have to push two rests, what reset are you talking about? Where are they located? First I assume you have a forced air damper motor, a motor located inside the front cover that is directly below the flue. If that is the case then the way the things works is first the vent motor comes up to speed which closes a switch that allows the spark ignition to light a pilot that intern heats up and allows the gas valve to open then the burners light. Then on most models a flame sensor senses the flame and the furnace operates as advertised.
See if you can find the flame sensor and clean it with steel wool. However, if the furnace is lighting abruptly and flame is blowing out of the chamber causing the resets as you call them to kick off, then I suggest you call a repair service. Give me a little more detail and I'm sure we can figure out what the problem is.

kurto 12-11-2008 04:58 PM

The two resets buttons are the "manual reset limit switch" (per manual). They are located just above the flame sensor. I think your description of flame sensor etc is correct. I will try cleaning the flame sensor but not sure exactly how to. The manual show the flame sensor being the tube coming from the valve which wraps around in a backwards C. There are 3 cone shaped protrusions attached to it. Is this what I try to clean, the inside of those? That is basically where the flame is once lit.

I did have a tech go out (used their "free" service call, probably to my detriment). He claims that because of dirty filters ( I had the old ones tenant probably never changed sitting there) and a dirty coil that the coil/furnace is ruined. Then he pulled the limit switch and showed me a small crinkle which he claims is a cracked heat exchanger. I was told that the exchanger was overheating, causing the limit switch to trip. Then I was told that the whole furnace needed to be replaced. This of course costs $2400 for a little 3 ton unit. That is bogus as I had my personal 4 ton furnace and AC replaced a year ago for that same price.

Now, I'm no dummy, I'd bet $100 that he if mostly full of crap. Though at one point early on he said he could acid clean the coil for $400. But soon decided this wouldn't even work and the only solution was a total replace. By the way, the unit is only 12 years old so I harldy think it is worn out.


And just before he left he claimed the gas valve was sticking. How do I check if the valve is functioning properly?

Could/should I just clean the coil with my compressor and shop vac the best I can? Not sure if anything the tech told me has any validity to it or not.

Thanks so much!

SKIP4661 12-11-2008 06:00 PM

I would get a second opinion on that heat exchanger, if it is defective it is probably still under mfg. warranty. I would also recommend removing the burners and blowing them out before replacing the gas valve. There is a good chance the valve is bad however.

NYCtinman 12-12-2008 11:28 PM

I agree with skip ( second opinion) about the heat exchanger -- as you mentioned gas valves do stick because of moisture,try taping the gas valve. Gas / utility company s wont tell you this because their in the business to sell gas not water.This is why most local codes require a drip leg ( to catch extra moisture)

kurto 12-13-2008 01:50 PM

Update:

I went to a local HVAC supply house and bought me some coil cleaner in aerosol form for $7. Cleaned coil (which was quite dirty). Tired to fire it up and was staying lit about 50% of the time. Cleaned flame sensor (which looked like a fairly heavy layer of dirt was ao the whole thing) with 220 grit sandpaper and now seems to be working fine - cross my fingers.

I'll post again if I have troubles again. Thanks to all who made suggestions.


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