There should be a Rating-Plate on the appliance showing the power in Watts - reach for your calculator and divide the watts by your household voltage - 230 in the UK and 115 in the US.
The answer will be the current the appliance draws - the breaker that trips may be supplying current (power) to the appliance and also other things also plugged into the same circuit - only you can check for this.
If the breaker that trips turns off all the power in the house then that's an earth leakage problem - an RCD breaker telling you about a potential safety issue.
You do not give enough information to provide a sensible answer - no make and model - no indication of which switches are tripping or their rating and no wattage of the pressing machine.
You may have had a defective presser but it's a bit unlikely that you have had two bad ones - there may be another defective appliance in the house - there may be a loose connection in the socket you plug the press into - two or more appliances together may be causing a combined current overload or a combined earth leakage.
I would guess that most steam press irons are rated 1kW to 2kW - not dissimilar to an electric kettle.
Good luck...
Peccavi, May 2010
