Hi I have a 15 yr old carrier weathermaker gas forced air furnace model 58sxa080 the furnace works fine most of the time although every so often usually in the mourning and sometimes during the day ( after the thermostat sets itself back to 65 overnight) when the thermostat calls for the furnace to heat things up to 72, the furnace is in lockout mode. I tried cycling the thermostat down past the temp reading on the screen and then back up, but that does not help. What we have to do is go to the furnace, turn the power switch on and off 1-3 times to reset the circuit board then it goes through the start up procedure and everything is fine for days. Last year the heat exchanger was replaced under warranty ( except for a 400.00 labor tab)due to water leaking out of one of the cells I have checked the air intake and exhaust for blockages, cleaned the water trap, visually watched the spark igniter and pilot cycle ,replaced the filter . Any help would be greatly appreciated thanks GREG

How old is your programmable thermostat. If it is as old as your furnace I would start with it. Is it a Honeywell 7 day programmable?

If you have a three wire pilot assembly that sparks to ignite you pilot it is possible that the bi-metal strip in the switch is not working properly. When the unit calls for heat it sparks and the pilot lights, the pilot then heats the strip and when hot enough set of points make and it energizes the gas valve, the gas valve itself has another heat strip in it that as it gets hot enough it opens the valve and the burners light. It is possible that one of, or both are not working as they should. Both of these items are rather expensive so I would not change them until I was sure that they were the problem. Remember this only applies to the pilot that uses the three wire pilot.
I just got my butt chewed out for not asking a person if his furnace uses LP gas, so does your furnace use LP gas??

letmetellu don't you just love the 3 wire pilot assembly with the pick and hold gas valve( one of the hardest to trouble shoot). gkscap give us some more info and we will try to help.

The thermostat is only 3 yrs old, yes it is a 3 wire pilot ,sorry yes it is natural gas, also there is a ticking noise I think from the gas valve when the unit starts and continues for a few minutes . This problem only happens when the furnace cools down from when the setback takes the temp from the high setting 72 or so to the overnight setting of 65 if the furnace is still warm at all and you manually call for heat it will work fine thanks greg

As T-Top says if you have a problem with the pilot and valve that we both think you might have is is very hard to diagnose. And you have to have a volt meter and know where to check at the right time to find out what the problem is. I would suggest you get a Tech to find out whet the trouble is. I do have to warn you that the parts are hard to find and are expensive. Over $60 for the pilot, even more if it I the gas valve.