Heater stopped firing. Blower comes on, tried 4 or 5 times, then stopped with Service heater light on. AGS light on. AGS switch has continuity, I replaced it, the high limit and igniter anyway. Now, blower comes on, does not fire, AGS light comes on and service heater light comes on. It only tries once now. New heater ordered and on the way. This one is 20 years old, and though it has run well for the last 5 years, it's time. I'd rather not throw it out, someone with less than myself may be able to use it.
Though there is continuity in the AGS circuit as well as the high limit circuit, I shorted them with paper clips and tried it again. Same result. Thermistor has to be OK, water temp is correct.
I pulled the control board off, and found a cold solder joint in the line of pins for the sockets on the end opposite the membrane connector. The cold joint did not appear to be one of the AGS pins. I re soldered them all. No change. Sound like a control board?