I have a rheem furnace and have recently encountered issues with unit not heating, correctly. And more noticeable at night when it gets colder, verified thermostat and its fairly new, verified led lights, and amber light comes when flame is on, but flame comes on for a short time and shuts off, never reaches thermostat set temperature. Checked for loose wires and non are loose. Can anyone please enlighten me. Thanks

When the flame comes on for a short while, are you talking about a few seconds or a few minutes,, if it's a few seconds you might try cleaning the flame senser with steelwool or fine sandpaper