Whats the maximum BTU/hr can my CB24 take?

My boiler is a 23.5 / 29.3kW - conventional non-condensing and I run 16 radiators and DHW to a storage tank with no problems.

I think the details of your boiler are...
Alpha CB24
Fuel Type Gas
Boiler Type Combi
Method Non-Condensing
Flue Type Room-Sealed
Fan Fan Assisted
Output (kW) 23.3 - 23.3
Manufactured From/To 2000 - current

So your BTU figure is 79,546 (kW x 3414 = BTU)

Peccavi
January 2009