Heater drawing more amps than rated

The current drawn by the heater is proportional to the supply voltage. Most appliance manufacturers will quote either the average current drawn based on the standard UK declared voltage of 230 volts. So for a current of 7.8 amps x 230 volts, the heater should be rated at around 1800 watts. (have a look at the specifications) In the UK the voltage can vary from around 216 to 250 volts, although 220-240 is the norm. As the resistance of the heating element is the only constant, if the voltage is indeed lower say 220 (or lower still) then the current drawn will increase a little; 1800/220 = 8.1amps It may well be that your property is suffering from lower than average incoming voltage as 9 amps would make it about 200 volts? As such you may wish to get this checked by your electricity supplier.