Six days ago my 1993 Janitrol GMP100 furnace failed to ignite. The igniter glowed and the fan ran, but there was no ignition. The technician we called replaced the igniter, but said we should just buy a new furnace since the root of the problem was the control board and Janitrol does not make those control boards anymore. I have found a few internet businesses that sell the control board for the Janitrol GMP100, but their prices vary by quite a bit - $89, $112, $136, $178 and $269 - which makes me wonder if there is any correlation between the price and the quality. (Perhaps the technician was right, I can't get a GOOD board for my furnace.) By the way the furnace still goes through spells in which the igniter glows and the fan runs, but the gas will not ignite. Should I try replacing the control board (an if so how much would a good control board cost), or am I better off replacing the furnace?

The glow is the ignition which seems to be working but your saying you should here a click from the gas valve and then it opens causing the fire. Try this make a jumper that you can put on the pressure switch easily. Now remember the pressure switch needs to be open when inducer motor starts then the negative pressure pulls in the pressure switch makes contact to its two terminals completes the circuit so when the glow energizes the gas valve opens to fire and also make sure there is a strong glow(bright red) because they tend to crack and sometimes ignite and sometimes not nothing to loose before replacing a board. God luck Mikie D.

The glow is the ignition which seems to be working but your saying you should here a click from the gas valve and then it opens causing the fire. Try this make a jumper that you can put on the pressure switch easily. Now remember the pressure switch needs to be open when inducer motor starts then the negative pressure pulls in the pressure switch makes contact to its two terminals completes the circuit so when the glow energizes the gas valve opens to fire and also make sure there is a strong glow(bright red) because they tend to crack and sometimes ignite and sometimes not nothing to loose before replacing a board. god luck Mikie D.
Ps Remember put jumper on pressure switch after inducer motor runs for 5 sec. Mikie D

Your furnace is getting to its end of life cycle due to age of 16 years old.

Circuit boards are available for your furnace and if you buy from a quality parts house or dealer there should be no problems but here again you should consider all the facts about the furnace age and how much you want to start spending on it to keep it running.