I have an Lennox closet furnace, GH6D-80FW, circa 1950's. It has a General Gas Valve B52. The furnace has worked well up to about a year ago. When I try to light the pilot, the flame will stay lit as long as I am depressing the red button (which you normally hold for 1 minute). I can even get the main burners to light, but only as long as I keep the pilot button depressed. My understanding is that the pilot flame creates a millivolt electrical circuirt on the thermocouple that activates a magnet, keeping the pilot gas valve open. I think this has quit working. I have replaced the thermocouple, but same thing happens. Is there a pilot valve replacement for this unit? (or magnet) If not, is there a complete gas valve replacement that I can retrofit on this furnace. I have pictures but not sure how to insert them here.

I have a York Diamond 90 furnace, which will only blow cold air, 4 flashes of red light on control board, what is my next step? I don't have an error code sheet, but from what I can gather 4 flashes means bad open limit switch. Where is the limit switch, how can I verify it is bad?