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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Lennox LSVFSD-NG gas log set, aprox 5 years old.

Customer Question

I have a Lennox LSVFSD-NG gas log set, aprox 5 years old. started this problem just before last summer turn off time. pilot light lights normally. may go off in a few days, but will go off within a couple of hours if the burner is turned on
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: 1 month last spring and 1.5 months now.
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: no, its just a simple installation, done when the house was build, hist on me. I am a retired aircraft mechanic (all systems)
Submitted: 21 days ago.
Category: HVAC
Expert:  Rick replied 20 days ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

This is a millivolt system. The pliot flame sensor (thermopile) generates all the power to operate the gas valve. It does this by maintaining a cold junction (temp diffential) between the tip (in the flame) and the "cold" bottom of the sensor. If a stray main burner flame heats up the cold junction the voltage drops out. A weak thermopile (they do "wear out") can also be the cause.