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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21386
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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The red light on my furnace indicates "limit switch open".

Customer Question

The red light on my furnace indicates "limit switch open". I'm trying to trouble shoot before calling technician
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year 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.

Is your filter clean? A dirty filter can inhibit air flow and cause this error. Also check the rollout out switches which are just outside the burner chamber (see attached for typical). Turn the power off then push the small reset button between the 2 wires. If it clicks you have reset it. If it doesn't click then it isn't tripped. Also check all the connections along the lead (from end to end) that connects to the rollout. If none of that works you'l probably have to call in a pro

Customer: replied 1 year ago.
I'm attaching a photo of the rollout switch I found. It wasn't tripped.
I changed the filter, but still getting the light for "limit switch open"
Expert:  Rick replied 1 year ago.

You could have a bad connection or possibly a bad limit. You need to check the connections on the lead that's connected to the rollout from end to end. The limit should be in that circuit. If you have a meter you can check for continuity across the 2 terminals on the limit.

Customer: replied 1 year ago.
I'll check and get back to you. I have a meter.
Expert:  Rick replied 1 year ago.

OK, also check continuity along this limit circuit where both ends connect to the board. It might save some time checking connections.