Can we converte combi boiler to works with propane?

To do so, you MUST get a conversion kit from the original manufacturer. They will give you a new rating plate which is their proof that this appliance is "certified" for use with that fuel. If you "Mcgyver" the appliance and try and convert it by changing orifices etc yourself, you will void the manufacturer's warranty. Also, the manufacturer will take no responsibility if this appliance hurts anyone or property is damaged because you have "altered" the appliance. Insurance companies will deny claims for the same reason.