Hi Namsag
I phoned Baxi and they stated that the fire front renewal compatible with 551 are s,c, w, p, w, lfe (as stated in the post above)
but compatible firefronts for 552 back boilers are:
gf3 super
sp3
pw 5
c5w
c5
I would like GF3 super or Bemuda SP3 as they look a bit modern...