Hey Guys It may seem that I might have forgotten crucial piece of info the row might not exist at all in the 2nd table hence why IsNull wasn't working.
ALTER Proc [dbo].[GetAmntPaid](
@QNo int)
As
Begin
Select IsNull(Quote.FullAmt, 0.00) - IsNull(Payments.AmountPaid ,0.00)
from Quote
Left Join Payments on Quote.QuoteNo = Payments.QuoteNo
Where Quote.QuoteNo = @QNo
End
This works perfectly
Regards