Corny keg foaming

[CoxR]

I have pulled out a keg I have not used in a long while and every pull is foam. When I fill the line with clear beer by pulling the handle and then release I can see the beer running back to the keg . I thought it was the tap but when I do the same and fill the line I disconnected the liquid out post and the beer in the line does not move. I am still not ruling out the tap but it is the only tap I have and did not have this problem a week ago with a different keg.
The only thing I have done since then was to run 1 liter of cleaner though the line and tap, then 1 liter of clean water through it.
Everyone who has ever kegged knows the joy and frustration that comes with it.
Right know it is the later for me. I was going to order 2 new taps today from Full Pint to start my keezer but work got in the way of that.
Cheers

 

[CoxR]

I forgot to add NO it is not over carbonated.

 

[pcmfisher]

How quickly does the beer appear to run back into the keg?
Is it that quick you can watch it happen?

 

[CoxR]

Yes I can see it, and it bubbles back to the keg

 

[CoxR]

Any ideas? I could try to transfer the beer to another keg but if there is something else I can try first that would be good

 

[N3MIS15]

I had this problem once. Mine was caused by a bad seal on the ball lock post.

 

[leighaus]

As in the poppet wasn't reseating properly ?

I think I have this issue at the moment

 

[N3MIS15]

At the time I replaced the post with another. It may be a seating problem I had, or maybe a seal/o ring problem.
I cant be sure because I never had a close look at the post, I had a spare on hand.

 

[N3MIS15]

The way i figured out it was the post was by moving the black fitting around (it was kinda loose), foamy beer seeped from around the fitting.
I put it down to being a cheap aftermarket fitting.