I must be going blind.

The first statement returns a "false" when not equal
Likewise the second.
The third returns a zero (0).
I need a Zero from each one (if applicable), instead of "false".
What am I overlooking.
I'm thought I've used this satisfactorily before, but I'm stuck now.

=IF(C6=E11,IF(C5=D11,IF(C3<=28,F11,0)))

Thanks in advance.