One yr ago, I replaced the flame sensor;
Now, after 12 mo. I get: 4 Flashes --Open temperature limit
On my Crane XL90 furnace; what's my best action plan now?

Take out the limit switch, tap it and blow of the dust and put it back in. If this does not work get e new one

Make sure furnace filter is clean. Restricted air flow will cause furnace to overheat.