Why does one hob have low gas when others okay?

I have a DF 600 SIDOm Stoves gas hob and electric oven. The oven is fine. 3 of the gas hobs have gas coming out as fast as normal but the 4th one (which happens to be the one where oil overflowed and spilt out of a fryer) no longer burns on full just a small flame. I have taken things apart and cleaned them (as much as I can) but it has not improved. Help!

CJ
November 2009