This could be a problem with your blend door actuator. I have included a link down below that is a troubleshooting guide to go through your heater and help you isolate the problem.
If it is the blend door actuator that is the problem, then here is a link on how to fix it:
If it is not the problem, get back in touch with us, and let us know what you found out. We will more than happy to assist you from there.
Monday, February 11th, 2019 AT 9:32 AM