Multiple VLOOKUP

I use this mulitple VLOOKUP to find a number value:

=IF(ISNA(VLOOKUP(A1,a,1,FALSE)=TRUE),0,VLOOKUP(A1,a,1,FALSE))+IF(ISNA(VLOOKUP(A1,b,1,FALSE)=TRUE),0,VLOOKUP(A1,b,1,FALSE))+IF(ISNA(VLOOKUP(A1,c,1,FALSE)=TRUE),0,VLOOKUP(A1,c,1,FALSE))

It returns the number correctly.

Now I want to alter the lookup from 1 to 5 to find a text value:

=IF(ISTEXT(VLOOKUP(A1,a,5,FALSE)=TRUE),0,VLOOKUP(A1,a,5,FALSE))+IF(ISTEXT(VLOOKUP(A1,b,5,FALSE)=TRUE),0,VLOOKUP(A1,b,5,FALSE))+IF(ISTEXT(VLOOKUP(A1,c,5,FALSE)=TRUE),0,VLOOKUP(A1,c,5,FALSE))

This doesn't work, I get #VALUE!

Strange thing is when I use

=IF(ISTEXT(VLOOKUP(A1,a,5,FALSE)=TRUE),0,VLOOKUP(A2,a,5,FALSE))

It returns the value ok.

The combining of the VLOOKUPS must have an effect.

Anyone any ideas on how to solve this?

Cheers