I have a harbor breeze ceiling fan with light. Last night my fan is suddenly staying on high speed. I select low speed and it goes to slow, but within a couple seconds, it goes back to fast.
Also the light sometimes goes on without selecting it.
I looked at the wiring to make sure all the fittings are tight and everything looks good. Any suggestions?

It may have the same code as another remote nearby, I would change code on transmitter and receiver to match.
Do you have more than one of these fans?
Did you leave the factory set code?