Hi,
so its taking the water in then it starts to drain the water straight away,is that correct?,
so basically its filling and draining nothing else?,
If that is the case, then theres a pressure switch which controlles the level of water in the drum.
if this pressure switch fails the machine will fill and empty and display the h20 error.
If the swich is ok then its most likely the main module has failed,
if this is the case best place for it is the skip,
the h20 error appears if the mains water pressure is below 5 bar,
as you didn't have this issue before you turned the water supply off,to change the valve,I suggest you check the pressure to the washer.
Turn the water off and remove the cold fill pipe from the washer and lower it into a bucket,
turn the water on and check the pressure,
make sure the water valve is fully open,
sometimes the valve can seize and although the head has moved the valve itself hasn't opened fully.
also there maybe a micro filter in the hose at the washers end,make sure it isn't blocked.
If the water pressure to the washer is low and doesn't fill in a specified time the machine will abort,due to a time out error and the h20 will be displayed.
Hope this info helps
good luck
paul, February 2012