Do I need a new boiler if I add radiators?

I have a back boiler supplying 1 rad in hall, 3 bedroom and 1 bathroom but need to add 3 new radiators and upgrade 4 of the 5 existing. Can this just be off the existing boiler for would the boiler need to be changed to accommodate the additional load? I am getting boiler engineers over this week but am sceptical that I will get an honest answer as fitting a boiler would be a more profitable job or the engineer. I would get it done if it needs it but not if it is not necessary as I did not allow for this when I bought it and would need to get a loan to pay for it.