The boiler relief valve
or the blow off valve is a safety valve that protects
your heating system from building up to much pressure
and possibly blowing up.
It's a very important part of your heating system.
Some times the relief valve or blow off valve will leak,
and naturally people assume that it is because the
relief valve is defective.
Sometimes this is true, and if it is leaking you should
replace it even though it is leaking for other reasons.
But it may just be doing it's job.
There are 5 reasons a relief valve leaks.