My gas heater ultra sx 80 (Manufactured by Armstrong Air conditioning Inc.) started to come on and off the other night. It would start up just like normal; flames would come on, but then after a minute or two it would shut-off. Next, the pilot would turn on again just seconds after shutting off. This would repeat a few times then the fan would come on for a few minutes then shut back down. I vacuumed out the unit, put in a new filter and it ran normally for an evening and now it will not turn on at all:confused:

Clean the flame sensor