Heater is not glowing, on Heat demand the blower comes on , you hear a initial click first but nothing past that point. Replaced the Honeywell Flame Rod Assembly as it was brittle and broke when checking it. Nothing. Tested the Pressure Switch (can) and it appears to be working correctly. Check voltage to gas valve and only read 13 volts when the unit is ON demand. My other unit will read at 24 volts at this point. I do not see any broken wires. What else can I check?