Latest Discussions : HVAC

Zimmie

11:18AM | 01/14/05
Member Since: 01/13/05
1 lifetime posts
Miller CMF 80 gas furnace. With PGB-DI Direct Ignition. I have a problem with burner igniting. It will lite for about 10 or 15 seconds then will go out. This happens 3 or 4 times and may start and work fine. Other times it won't ignite at all and I hear a motor running with no flame in fire box. I also at times have to turn down the thermostat and reset it to 70 for the furnace to come on. ( it has a new thermostat ). As I write this the furnace is working fine, but may not come on the next time I need heat ???? Thanks for any help. Zimmie

JGRIZZ

07:50PM | 01/14/05
Member Since: 12/16/04
54 lifetime posts
All electronic igition systems have flame rectification, or a means of proving there is a flame present in order to keep the main gas valve open.

There are various means of flame rectification, if you have a flame sensor the flame sensor is a rod with one wire that goes to it and it is usually mounted on the burner box that holds the burners.The other type of rectification method is made through the hot surface ignitor such as one an older rheem unit. I would guess you have a flame senor rod.

There will be one white wire connected

to the top of the flame sensor and the wire will go from there all the way back to the ignition control.

There will also be two white wires connected to a plug-opposite the flame sensor, these two should lead back to the hot surface ignitor. Dont touch the hot surface ignitor!!It will break from the oils on your hand. THe flame sensor only has one wire on it and the opposite end of it sticks into the flames from the burner outlet. What happens is that the igniton control sends a signal from its ground lug through the furnace cabinet ground, and the signal travels from the burners across the flames to the sensor and back to the ignition control.

A few things can cause what youre talking about. A bad, or loose or dirty ground. No ground at all. Improper polarity, a bad or dirty flame sensor. A bad ignition control or even a bad sensor wire. Usually the ignition control will look for a signal from the flame sensor and if it does not recieve it in about 2-5 seconds it will shut down the unit and it will try a few more times to ignite.

Another possibility is that the gas pressure is too low, and another could be that the burners are not lined up properly.

I would suspect a bad flame senor first and would attempt to clean it or replace it first. Other than that you will probably need someone outhere who can diagnose a flame rectification problem.


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