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Rick, HVAC Supervisor
Category: HVAC
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Experience:  40+ yrs. experience as a licensed oil & gas technician.
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I have the same issue on a Carrier furnace showing error 34

Customer Question

Customer: I have the same issue on a Carrier furnace showing error 34 but the flame sensor appears clean (and I cleaned it anyway, twice). Flame starts up then shuts down after 3 seconds, does it 4 times then soft lockout. I'd like to rule out the flame sensor (bypass it to test) and then rule out other issues. Stopped working the first night of the big snow around here, so suspicious that had something to do with it also.
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Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

You can't bypass the flame sensor. You can check it's output with a digital multi-meter that can read micro (not milli) amps. It's possible this could be a draft issue but it's acting like a flame rectification (sensing) issue. Check to be sure the exhaust isn't blocked with snow. Also check to be sure the condensate drain is not clogged

Customer: replied 1 year ago.
Can you call to walk me through checking those other two issues? (###) ###-####
Expert:  Rick replied 1 year ago.

A phone call is an additional charge and I'm not available for a call now. We can continue here if you like. I need the model number of your furnace if you want specifics on checking the condensate drain. Clearing snow away from the vent is self evident. Do you have a meter that can read micro amps?

Customer: replied 1 year ago.
No meter unfortunately. The model is Carrier 58mxb100-f-10116. A Comfort 92. Where would the exhaust vent be?
Expert:  Rick replied 1 year ago.

The exhaust vent is connected to the small draft inducer fan on the front of the unit. You'd have to trace the path of the vent to were it terminates outdoors. Give me a few to look up the specs for this model.

Expert:  Rick replied 1 year ago.

Here is the manual for your unit

Condensate drain configs start on page 7. You need to be sure water can flow out of the collector box into the trap then out of the trap to a drain. You'll have to disconnect whatever hoses you need to check/clean the drains

Customer: replied 1 year ago.
Ok this will take me a few min. Just unhook tubes and see if there is debris? Dumb question, if the condensate drain is stopped up would I get error 34?
Expert:  Rick replied 1 year ago.

A 34 error is a flame sensing error but a drain blockage can and will also cut the burner out after it fires up and since you don't have a meter you can't test the flame sensor. Double check the flame sensor connections. You may have to replace it.

Customer: replied 1 year ago.
I've checked the connections. Unfortunately we are snowed in with no heat and no one can get to us. I will check the drain -- no way to fool the board regarding the flame sensor (so we could get even an hour of heat)?
Expert:  Rick replied 1 year ago.

No way to fool the board and that's a good thing. You could blow your house up if there was a way to bypass the sensor. If you're snowed in then the vent and condensate approach is probably your only shot at getting this running