Concatenate Function To Join Some Text Strings To A Cell On A Different Sheet

I have been trying to use the concatenate function to join some text strings to a cell on a different sheet - From an input sheet -Sheet 1 named Input, to a Notification Form (Sheet 2). Although the Function Argument display tells me that it will display the result I want it actually displays just the formula. It's a very simple thing

Address 1 10 Downing Street
Address 2 Westminster
Address 3 London
Postcode SW1A 1AA

I want displayed as: 10 Downing Street, Westminster, London, SW1A 1AA in a single merged cell. All I am getting on the Form is =concatenate(Input!c25," ",Input!c26," "Input!c27," "Input!c28). I feel sure that it is a very easy solution but I can't arrive at it!!