Lennox G60UHV-36B-090-10 primary/secondary limit switch test?

Old 10-21-12, 11:23 AM
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Lennox G60UHV-36B-090-10 primary/secondary limit switch test?

Hello everyone. I have a Lennox G60UHV-36B-090-10 furnace that will not start-up. It flashed red led error code 3-1 which the panel says is the primary/secondary limit switch open. The furnace is just over a year old. Can someone please tell me how to test this switch and also whether something else could trigger the same error code? Also are there two switches I should test?

I have recently replaced the thermostat for a Nest unit could this have done something to the furnace? The furnace is getting a start-up command when I send it from the thermostat and I can see the combustion air fan start to spin up behind the top panel but it stops spinning after 3-5 seconds and the furnace does not fire up.

The furnace main fan continues running indefinitely but the furnace will not restart.

I have replaced the filter and can't see any other obstructions.

Thanks in advance.
Old 10-21-12, 03:06 PM
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Does the furnace blower run?
Old 10-21-12, 03:32 PM
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Check the limits for continuity with a multi-meter. If you don't know how to do that, call a pro.

Generally safeties don't open for no reason (whether it's the primary limit which should reset by itself or a rollout switch).
Old 10-21-12, 07:03 PM
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It has several limit switches, one even at back of the blower. You'd better call a pro.

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