Error with IF Statement

I'm using the following formula to work out any variances on workers timesheets.
=IF(SUM(E4:G4)=0,0,(E4+F4+G4)-(B3*4))

E4 - Hours worked
F4 - Holiday hours
G4 - Sick hours
B3 - Weekly contracted hours * weeks in the month

This works fine until I try and adapt the formula for employees who work term time only.
I have simply worked out which weeks they will be off and not counted those weeks in the formula.
e.g. they will only be working 3 weeks in October so I used:
=IF(SUM(E4:G4)=0,0,(E4+F4+G4)-(B3*3))

This gives me the error 1.42109E-14

Does anyone know how I can get this to work?

Edit - I've just tried multiplying it by different numbers and it works with them all apart from the ones I need?