are you trying to run a lpg(bottle gas )version on mains gas if so this is not possible without jet conversion back to nat gas.
or you may have a problem with the bayonet hose not being connected and locked properly which can give a poor supply pressure.
or you have a poor supply pressure to the cooker in the first place.
i doubt it is a problem with the gas taps as they are all giving you the same fault
maddog, September 2007