A Google search turned up the following thread on hvacmechanic.com forums:
We have the same issue as NRoger:
"The main burners on my Carrier 58SS run for about 15 seconds, turn off, then repeat. From reading on this site, I suspect that the flame sensor is at fault, and would like to clean or replace the sensor. Can someone tell me where to find the flame sensor on this unit?"
Is NRoger correct that this issue is caused by the flame sensor?
What is the procedure for cleaning accumulated soot & carbon from the safety element / sensing probe / flame sensor? I have all the original owner's, service, & part manuals for this unit. However, this procedure is not explained in detail. The pilot mounting bracket and burner assembly obstruct one's view of the flame sensor. I imagine one has to remove the pilot assembly to clean or replace the flame senor. Is this correct?
Should the sensor be replaced rather than cleaned? It is still the original part.
Or should we consider replacing the entire furnace since it is now 23 years old? I replaced the main blower in 1998 and the induced draft motor in 1999 myself. What is the life expectancy of the heat exchanger?