Munchkin piping for other boilers

Dof3

I piped a Laars Mini therm the same way as I do my Munchkin boilers[as per Munchkin install guide] only I used a 4-way mix valve between the ret and supply water. I cannot get the boiler to heat the slab. This is for an infloor job in a basement. Is this not a good P/S for this type of boiler. It works great on all the Munchkins I have installed. Most of the time I just use a loop primary and then close space my t's for the secondary. Any help or should I just take it all out and use the old way?? Thanks for any help.