Combi boiler showing EA no heating/hot water

[Mosaic]

I run the CH constantly on a v low temp so there is no 'cold' period. Some time overnight the combi boiler has stopped working and the display is flashing EA. Gas supply, gas & water pressure, electricity supply all fine. I have restarted several times and get P1 -P2 - P3, then temps will start building to maybe 17C, then it knocks off to EA again.
Have got a guy coming sometime in the next 12 hours.......
Wondered if anyone can suggest anything - I'm guessing this might have to do with very cold water from the mains as it was a touch parky outside last night. All suggestions welcomed. Thanks in advance.
Please excuse but I've also posted on 'how it works'.

[tamborine]

download the PDF page & read p.26

http://www.google.co....cial&client=firefox-a