lennox constant outage

[operator]

new customer calls to have frnc looked at, while there can you check fireplace

lennox about 7yrs old keeps going out

previous company changed thermopile and thermocouple, removed piezo(why I dont know, nice to remove glass to light pilot)
previous company was found through lennox

neighbour has the same furnace with same problem
she is sending me the invoices from previous visits

they dont have any wind to cause an issue
direct vent

main flame will die for unknown issue, will run about an hour give or take. say they can toggle the switch and will come back on most times

I told them I dont do much work with fireplaces but would ask questions of the guys that do

so, any ideas
(can post mod. ser. tomorrow)

[blk]

Millivolt loss thru switch if only main burner is going out and pilot is staying lit. Pull your volt meter out and check all of your readings...open(no load), closed (under load)power at valve, valve opening, loss thru limits, loss thru t-stat(switch)circuit.