our houses usually put 20A breaker n corresponding wire gauges for aircond n heaters

3.6kW is the norm n for good reason cos there's some tolerance>3600W/240V=15A

if u up the appliance to one with a higher current draw, for e.g. a 4.8kW one, then>4800W/240V=20A

assuming u run the heater at full output n for a prolong period of time, this means u r running the heater at or near the tripping threshold of the breaker n the wires r gonna get warm pretty fast - a potential fire hazard waiting to happen

if die2 must put more powerful heater, then change out all the 3 wires to the MCB with lower gauge (thicker) ones n the breaker itself (mayb a 30A class B one)

Can oso install an individual RCCB at the heater termination point for added peace of mind