Hi everyone, I wanted to add to this very old post as I had this exact problem and read everything posted in numerous sites and eventually sorted the problem and thought my experience and methods may help someone else.
Recap of problem: installed about 6 years ago, best shower ever, I have aqualisa in both bathrooms and have had them in the last 3 houses since 1996 and never a problem.
Took a shower, switched water off between soaping and that, switched back on to find no hot water coming through and blue light flashing, left me very mad and very soapy!
Tried to research the answer, this site had exactly my issue but not the final solution for me.
First stage - ensure you have not turned off any water supply then Try turning on and off at the mains several times - no effect for me but I understand this has worked
Second stage - remove the on off dial module, remove, dry and clean the black socket, replace and turn on - no effect for me but understand this has worked
Third stage - remove shower head from hose and allow to dangle in bath or shower tray, go to the pump processor in the loft and shut off the cold water isolation valve on the cold water.
Turn the temp selector to fully hot and press on button, initially a few litres of water will come out but the pump noise will change and the water flow tends to stop. VERY IMPORTANT NOW TURN IT OFF. Do not let the pump run dry or I repairable damage will occur. Allow the processor to stand for a while and if close you may hear the processor recharging itself, then turn the isolation valve for the cold water back on.
Turn the temp selector to mid way hot then switch on.
This action worked for me and I assumed here was some form of air lock or pump malfunction.
I hope this works for others.
Aqualisa showers rock!