blow off is very slow

slow blow

do you mean the drain from the boiler, or the low water cut off is slow.
if it is the low water cut off, then i recommend getting a pro in for service, as it may be unable to prevent your boiler from dry-firing, and destroying boiler, and building with it! if it is the boiler drain itself, then that is a problem which can wait for warmer weather, to "clean out the mud legs"; although it could save fuel to have it done sooner. --nbc