burn marks on the bottom of the mash pot

All grain ,step process ,false bottom ,why am I getting burn marks on the bottom of pot,temperature not above 152 degrees ?

You must be heating your mash tun from the bottom, I presume?  Maybe with a propane burner?  The temp in the vessle may be 153 but if you do not have good circulation of the bottom layer it would be prone to burning.

Thanks for your input .yes you are correct ,using a propane burner . How can you possibly stir with a false bottom?

The best way to stir it is to use a march pump to pull the wort out from the bottom then recirculate it up to the top.

X2 on the March pump.  There really is no other good way to circulate with a false bottom.  The impellers on March pumps are sealed and magnetically coupled to the drive motor so contamination from the pump bearings is not an issue.  Expect to pay around $150 for one.  A low cost alternative would be to heavily insulate your tun so you can get away without heating/recirculating.