I have a13 year old Plus 80 Model 331AAA which will stop for no reason. Shows error code 14 when it stops. Furnace has been thoroughly checked twice in past two weeks by technicians and they can't find any reason for the unit to stop. If I turn off the power switch on the side of the unit for a few seconds and then back on the unit fires back up and works normally for a while. Unit will also recycle after three hours.Then it stops heating again. No real pattern to this, sometimes in two hours, sometimes in two days. Hot surface ignitor was replaced 1 year ago. Filters are clean and the unit is clean- techs say everything else appears normal. They checked the flame sensor and gas valve- both OK.

Any suggestions? They also visually checked circuit board but found nothing.

You have safety switches that will cause the furnace to stop working most of these are manual reset but there is one that is automatic reset and that is the limit switch that is on the fire wall of the furnace. It is a insertion type switch that is about three inches long, mounted with two screws. This is a bimetal switch that gradually loses its tension and changes the temperature at which the furnace will cut off and on. This is not a very expensive part and is worth trying to see if this is the problem.

One other thing, you said the furnace is clean and the filter is clean, are you sure that the Airconditioning coil is not dirty and possibilly causing the same problem as the limit switch would cause.