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mike schwa 03-14-2013 08:56 PM

carrier 58mxa problem
my lp furnace comes on and runs for about 10-15 mins until it stops burning. fan keeps running but burns shut down with a code 33. changed air filter and cleaned out burners with no luck. bad sensor???

old_squid 03-14-2013 09:28 PM

Close any supply registers? Cover up any return registers lately? Do anything to the furnace lately that would have changed the fan speed? Do you have a zoning system with multiple theremostats? Do you have central air conditioning and has the coil been checked to see if it's dirty?

mike schwa 03-14-2013 09:32 PM

one zone and one t stat. closed and limited a few vents several months ago and problem started yesterday

mike schwa 03-14-2013 09:34 PM

do have ac and returns are open as been for months

mike schwa 03-14-2013 09:40 PM

fan speed is the same as been seems like. coil; for ac? havnt checked that. would coil change fan flow?

how 03-14-2013 09:45 PM

Usually with a 33 code either your limit is triggering or a roll out switch is.
It can be because these controls are faulty or because they are doing there designed job. You need to meter each one to find out which one is opening and stopping your current.
Let us know what you find.

mike schwa 03-14-2013 09:49 PM

limit switch is triggering. has little reset button on top of it that I push to start burning again after turning off main power supply.

how 03-14-2013 10:11 PM

Resets usually only apply to roll out switches. Is this control situated near the burners?

beenthere 03-15-2013 04:59 AM

As How said, sounds like a roll out is tripping, or a blocked flue switch, not your high limit. So problem could be a bad or clogged heat exchanger, or a clogged/restricted flue.

mike schwa 03-15-2013 05:17 PM

respond to "how". yes this limit switch is on top of metal box where burners are. not directly ontop of burners but back a littile by intake side of burners. little round brownish switch with reset button on top of it. push reset on switch and furnace will light again.

mike schwa 03-15-2013 05:21 PM

my manual calls it a rollout switch. I work on motorhomes and the switch is very familaer as "limit" that's what the rv world calls it on furnaces and waterheaters

how 03-15-2013 05:31 PM

That's a roll out switch to protect against flame & heat not being drawn properly through the furnace.

Either the switch is faulty or you have a situation where the furnace is over gassed, the exchanger is partially obstructed or a cracked exchanger pushing flames towards the exchanger opening.

If you have other roll out switches on the same circuit, you can swap them if they have the same listed heat rating. If you then still get tripping in the same location as the old one, you have other problems to check out. If the roll out switch that was tripping before, keeps tripping in the new location, it's probably a faulty roll out switch that needs to be replaced.

beenthere 03-16-2013 02:09 AM

Check your hat exchanger. Roll outs only get weak, if they have been running at temps close to their trip setting. And that only happens when there is a problem.

mike schwa 03-16-2013 05:48 PM

had someone look at the heater and he says its the inducer or exchanger. says the exhaust is weak and not pushing enough air thru to keep burner from overheating. 700 bucks for inducer and or exchanger at 1600 bucks!!! sound correct? isn't it summer yet!!!!!!!!!

beenthere 03-16-2013 06:09 PM

He should have been able to determine which it is. Would hate to pay for one and it be the other that was the problem.

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