Been trying more with various combinations of 1-wire, WM928 and WD. No success. one of the main problems is that WD cannot see the WM928 if there is no barometer module attached. This is not the case with any of the other modules. When run simply as a 1-wire station on an old machine it gives a different pressure, and all seems to be well. I will try plugging the WM928 into the other machine briefly tomorrow to see if it makes a difference. i will post the results after then, although any suggestions would be welcome.
Best wishes
Mike