what does fault E.25 mean?

we have just installed a new radiator , turned on the boiler and have a fault message reading Fault E.25 . it goes to start then turns itself off. We have put the water back on and bled the radiators but we get the same reading. Its also affected the shower. Please can you explain what the reading means and how can we fix the problem. The boiler is a Vaillant ecomax 824/2E