From the fault you describe then its going to be the timer unit as they do play up like this and fail im afraid.
Now yes this can be fixed as the timer is still avalible to buy. The part itself is £80 so not a cheap part. But if you need an engineer to call and fit it for you then you can add another £60 on top of it so roughly around £140 for the repair.
Hope this helps you. If you need anymore info just get back to me.
The part number for the timer is###-##-####/p>