We have had a similar problem; we had a faulty valve which may have overloaded the relay outputs or we think there may have been a short in the wiring. The gas engineer who wired the thing originally made an appalling mess and there were bare wires all over the place!
Did this fault just happen all of a sudden or had you recently modified the wiring or changed anything before it failed?
Prior to this fault we were very pleased, it's useful to have the 7 day timer as we work during the week and finish early Friday so it's handy to be able to set separate timings on Friday and the weekend. The battery back up and backlight are very useful!
I am going to buy another one as there are no alternatives - hopefully we will have more luck!