Feet burning during long rides

Hi all,

I am sure this is a common problem and if there is a thread out there someone knows of, I would love to be connected to it. 

I am training for IMLP this year and have had new long bike distances My feet never had an issue before but now for rides over 3.5 hours they are burning.  Does anyone have any advice? I do have orthotics in them and they have worked fine until now.  I thought I heard somewhere that the burning is caused by too much foot movement but I'm not 100% on that one

Thanks!