New boilers are less tolerant to iron oxides (sludge) than older boilers.
The favoured options are generally to cleanse (power flush) the existing system boiler before replacement.
Various devises are now on the market which will provide a 2nd tier of protection for the new boilers
They offer further protection by using a magnetic field contained within a vessel or vortex technology.
These collect any oxides and foreign objects for removal during the annual service visit.