Gas and Oil Home Heating Furnaces - Burner cycles on and off a number of times before blower comes on

I have a Carrier furnace approximately 20 yrs old. Recently, I've noticed the electronic ignition comes on and shortly afterwards the main burner ignites. The burner remains on for about 10 - 15 seconds and then shuts off. A few seconds later the burner will re-light stay on again for 10-15 seconds and then go off. Usually on the 3rd cycle, the blower fan will come on, the burner stays lit and the furnace will continue until the temperature has been reached.

I don't remember the furnace doing this in the past and I'm trying to get an idea what might be causing this before calling a technician, in the event I am unable to determine the cause and repair it myself.

Any recommendations?
Thanks Richard

Well, looks like whatever was wrong has progressed to total failure.. nothing happens now when I turn the heat up..

I've got a call in for service.. should be interesting to see what went wrong.

Possibilities include a bad flame sensor or bad circuit board. Perhaps the furnace went into lockout.

I also have a 20 yr old Carrier furnace (model 58DHB propane) that has been doing the same thing. I had a repairman look at it and he told me these older units were difficult and expensive to fix. It started to work when he was there so he left and didn't charge me. This furnace does not seem to me to be antiquated or wore out.

I have replaced the 3 wire pilot switch and checked out most of the components. I finally found the problem by bypassing the solid state lockout timer. The timer doesn't lock out very often but it shuts off the main gas burner several times when the furnace is running. Right now it seems to be locked out. A new timer is $200 and I want to be sure it is the timer and not the signal going to the timer before I replace it.

The timer connects to the gas valve MGV terminal 1 and to the gas valve terminal 2. Does anyone know what terminal 2 is for? And what is the signal that is supposed to lock out the timer?
thanks!

Can anyone explain what the purpose of the lockout timer is. I need to see if it is working but I am not sure why it it there.
thanks

Can anyone explain what the purpose of the lockout timer is. I need to see if it is working but I am not sure why it it there.
thanks


Carrier at one time didn't have a lockout circuit. If somethings failed, it might cause the pilot ignition system to cycle on/off repeatedly or the pilot to stay lit but the main burner to not turn on. When they reengineered the furnace they combined the old spark ignition system with the lockout feature, which just turned things off if something wasn't working properly.

Unfortunately, it tended to be the lockout feature that went bad on those boxes (usually gray plastic), wjen other parts of the the furnace were OK.


Loook for a distributor of Carrier, Day and Night, Bryant or Payne ---all brand names using that same part.

Thanks Seattle. It does strike me as overdesign. If they didn't have logic circuits (and the incredible design choices it provides) they never would have put that lockout device in the safety circuit. But there must be some 3 mile island scenario that they were trying to assure never happened. I would like to know what it is.