Blocked top tap on a king keg?

[HantsBrewer]

Greetings all

I currently have a Brewferm Dark Abbey beer in my king keg which has been sitting pretty for the last month or so since transfer from the FV. Last night I attempted to draw off a pint, but after only half a pint the pressure suddenly dropped off and the output was reduced to a trickle, and then nothing at all. Of course my first thought was that maybe the seals are leaking, but then surely there would have been no pressure in the barrel to start off with? Please note that the O ring was well lubricated, as were the threads.
I then gave the barrel a squirt of CO2, left it for 10 minutes but there was still nothing coming out trough the tap. I tried another squirt of CO2 and opened the tap immediately after, but this also resulted in nothing coming out. The only conclusion I could draw from this is that the seals are OK but somehow the top tap has become blocked. Has anyone come across this problem before?
Ideally I'd like to save the beer as the half pint I did manage to draw off tasted pretty good, so if the keg seems beyond hope then would bottling be an option at this stage of maturation (1 month)?

It's worth noting that I almost forgot to put priming sugar in the keg. I usually dissolve the sugar in boiling water before priming the keg, but this time I dissolved the sugar in cold water due to the fact I'd already started siphoning when I realised what had happened.

I have had mixed results with this keg before. I had a Nelson's Revenge which created no pressure whatsoever and ultimately went bad. I have also had a Coopers Bitter in there which was extremely lively and managed to maintain high pressure right down to the bottom.

Thanks in advance for your advice.

[Lillywhite]

If you're convinced you have pressure, which you can check by squeezing the brown rubber on the S30 valve then you have a problem with the float system fitted to the top tap. It may have come adrift from the back of the tap.