something else ive just thought of, now you may not of touched this but il tell you anyhow for future reference, if you,ve ever removed the heater box from under the bonnet to get to the ecu,s (most people have) theres 2 earth wires together right by the wiper motor (you cant miss them) the one is an earth for the heater motor obviously and believe it or not the other is an earth for the ecu! i use to think it was an earth for the wiper motor but it isnt, so my point is,if you have had the heater box out recently check that earth point to make sure its tight and not loose,also might be worth taking the screw out and cleaning the connections and body with a little sandpaper there, a bad earth there could be half or all yr problem

i had the heater assembly out the once and those earths off and couldnt work out why i had no spark doh!! lol.

heres a pic so you know where i mean,hope this helps.