Mansfield frost proof sillcock leaks at packing nut

raz

My Mansfield frost proof sillcock leaks around threads of the packing nut and at stem only when backpressure is applied by leaving charged garden hose attached. I've replaced packing and packing nut O ring twice with no joy.

I realize leaving a charged hose attached is not a particularly good practice, but I used this sillcock with a hose timer all last summer with no leaks at all and just don't understand the current problem. Anyone have a guess at cause of leak and suggestion for repair? Thx in advance!

TheEplumber

Are you sure it's not leaking at the vacuum breaker located on top of the bib?

raz

I'm certain the leak is from the threads on the packing nut/stem; FWIW, I've also flipped the washer in the vacuum breaker and then finally replaced with new kit - all to no avail.

What do you think about beefing up the packing bonnet washer with some graphite packing thread?