I am on propane which was down to 30% yesterday but is full today. My problem is my heat will not come on, the fan works in the on position. The LED flashes a 31 . I have replaced the thermastate and checked the breakers and fuze and they are OK. I just don't know where to go from here. I am hoping for some quick advise. Thank You.

Read all this link.

https://www.askmehelpdesk.com/heating-air-conditioning/carrier-weathermaker-8000-a-182116.html?highlight=carrier+codes

Make sure you have LP in your tank. Code 31 is pressure switch did not open or close. With LP you should have an extra pressure switch in the system to cut out if the gas pressure it to low.

Now that I have a full propane tank, I was hoping that would have fixed the problem. I was wrong. Is there something I can do to reset or ? I still don't have heat.

Turn the power off going to the furnace for a few seconds to reset the control board turn it back on and give it a try.(main power going to furnace 120v)

I did turn off the power, nothing happened. I also cleaned the return vent filters and put them back in. they were not that bad. Anything else I can try before calling in the expertz?

You can remove the pressure switch and blow and suck lightly on the rubber hose going to it to see if its stuck. You should hear a click from the micro switch when doing this. Put it back together and give it a try. If it gives you code 31 again after the previous test you may have a bad control board.(TURN POWER OFF FIRST)

How do I identify this pressure switch (locate) so I can blow and suck through it?