Isx 15 cm2250 regen advice needed

[Rawze]

Don't guess at it .. pressurize the coolant system to 20 psi, find all the leaks and fix them.

Find and fix your exhaust leaks while your at it... that thing cannot regen properly if there are exhaust leaks.

Also check/clean the doser injector and exhaust components involved with the regen process. that DPF was a good start, but it is far from the only thing that typically needs to be done to get the systems working properly again after such neglect.