How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22515
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

Furnace ignites and stays on for 5 sec then shuts off for about

Customer Question

Furnace ignites and stays on for 5 sec then shuts off for about 30 sec. Tries again and shuts off again. Does this five times and quits. Unit is a natural gas Carrier 58PAV070-12. Also LED on furnace blinks {short, long, long and then repeats.} Tstat is White Rodgers #1F78 basic, nonprogrammable. AC part of system has run fine. Squirl cage blower and upper exhaust blower run fine before glow plate and gas come on. Any thoughts for me to try? Thanks
Submitted: 7 years ago.
Category: HVAC
Expert:  BillyHvac replied 7 years ago.
Have you sanded the flame sensor yet?
Customer: replied 7 years ago.
no where is the flame sensor?
Expert:  BillyHvac replied 7 years ago.
in front of the burner at one end is the ignitor, at the other end is a metal rod with a white porcelin base. Sand it off with emery cloth or steel wool, even if it looks clean. A glaze can develope and impede flame sense thus shutting down the system. re start and wait 90 seconds for results.
BillyHvac and 2 other HVAC Specialists are ready to help you
Customer: replied 7 years ago.
The flame sensor is cleaned flame is on it, but still kicks out after 5 seconds. What next?
Expert:  BillyHvac replied 7 years ago.
Ground issue. Check that control and furnace ground are good..check all the way to breaker. Then we can move to pressure switch
Customer: replied 7 years ago.
Grounds appear to be good. One screw was a bit loose but everything looks solid now and function is still the same. Please what's next?
Expert:  BillyHvac replied 7 years ago.

now locate pressure switch. It has an rubber tube and 2 wires to it. Remove 2 wires, start furnace, wait for exhaust fan to start and touch the 2 wires together so they make contact and hold them that way and see if unit progresses.


I will be off line for a bit but will respond as soon as I get back

Customer: replied 7 years ago.
Found the pressure switch. When second or exhaust fan came on I connected the wires that were connected to the switch. (It was round and did have a rubber tube going ditectly to the heat exchanger wall.) Unfortunately function remains unchanged. Still just 5 seconds of heat. What's next?
Expert:  BillyHvac replied 7 years ago.

Here is a manual for your unit. -


Frome here out the test require checking micro amps of flame sensor. If sensor test good replace circuit board. If sensor does not test good replace sensor

Customer: replied 7 years ago.
How many microamps should the flame sensor show? Only one wire goes to it so current from what to what and would this be while the flame is on it? Is there anything else to try other than the circuit board if the sensor tests ok?
Expert:  BillyHvac replied 7 years ago.

Hello again...


the sensor should read at least .5 ua. The meter set for DC micro amps, one meter lead to sensor and other eter lead to where sensor was plugged in. If .5 and above replace ign control. You can also add a wire from the burner to the ground terminal on the control

Customer: replied 7 years ago.

We do not have the furnace working yet but Billy went out of his way to help. We still have something to try that he gave us. My husband wants to make sure Billy receives compensation for all his help. I think the last thing he did was getting us the manual for the furnace. Which may still hold the answer to the problem. We are pleased with the service we received and will recommend the site to others, or use it again for any further problems. We were not able to work on it today and will not work on it on Sunday. If there are further questions we will contact the service on Monday.

Thank you for all your help


Expert:  BillyHvac replied 7 years ago.
I thank you very much! Happy Holidays!

Related HVAC Questions