How can I fix RF1 as heating won't come on? ?

I have a Digistat RF1 and SCR on wall. Earlier today we had a short power cut. Now the heating won't work. I have reset the rF1 so that everything looks as it should re lights etc. the only thing not working is the boiler not firing up. However when I switch the hot water on to continuous the boiler fires up briefly then goes out. This only happens with the hot water not continuous heating. The plumber is coming in the morning but I was hoping someone might have an idea or do you think we need a new Digistat? The Worcester boiler (3 years old) is working perfectly and was serviced in summer. Thanks