BAXI 105e, DHW Strange issue

[Plipplop]

I have a very strange issue with my BAXI 105e DHW. if i turn on the hot tap the pump starts and demand for DHW is shown, after a some seconds it will show an error, 60 degree, pump or flow. Well switch the tap off wait maybe fifteen seconds turn tap on and low and behold hot water. If after a central heating cycle and boiler is on and fired if you then demand hot water, delivers as expected because boiler has fired. Have checked venturi, no dirt or damage - cleaned and replaced, have checked diverter disassembled checked all looks ok and operates. All microswitches seem to operate as they should. Can anyone suggest what I am obviously missing, is there anywhere a flow diagram of the whole process I could look at. Your help would be greatly appreciated

 

[cjg]

faulty diaphram with the sound of it.