[clogistics]

Intermittent pilot assembly
White-Rodgers type 5059-122 pilot relite control module
White-Rodgers Liquid Mercury Flame Sensor, 48" Element, 3 Pin Plug In
White-Rodgers 36C94-213 gas valve

The furnace want cut on automatically, I normally just manually light the pilot burner and the pilot will come on, because the pilot relite module want activate a spark. So when the system is started manually everything engages normal, but when the thermostat reaches about 70 degrees the whole system shuts down accept the blower, an I regularly have my thermostat to cut off at 75-80 degrees, so while the blower is still going the whole system will reengage itself back on in about 2 mins completely. An this continues to happen until the temp reaches the thermostat temp, an once it reaches that temp the system no longer comes back on until I manually light it again. So what could be the possible reasons for this occurring. If you’ll need any more info let me know. Thanks a lot

I’ve cleaned the thermostat, control module, flame sensor contacts and tighten a few loose screws, still same results.

 

[beenthere]

Dirty air filter or evap coil may be causing the high limit to trip.

 

[HVACTECH96]

bad mercury sensor.be better off in long run replacing furnace because mercury sensor is pricey and if you start messing with old one it will probably break, and then you have to deal with mercury spilling on floor.