Thanks for the reply Donald. I looked around and found that R5 (100Ohm) was high impedance. Strange. I don't think it could have blown in-circuit as the Op-Amp is limited to 30mA output. Anyway, I simply shorted R5 and the circuit now works, giving a full scale variation of ~7V to ~31V, corresponding to 2V-0V DAC output respectively. I'll probably just leave out R5 in the final circuit.
Thanks again for your input.
David.