I have a 2 year old EcoTec937. If you run the shower all is well for the first 10 mins or so, then it seems as if the water in the charging tank seems to run out and the boiler does not seems to be able to keep up with recharging it quick enough so the water goes cold (not stone cold, but cool enough to be unpleasant for a morning shower!). The tank does seem to recharge quickly if you switch off the water for a few minutes - it just cannot keep up with any reasonable sustained flow of hot water.
has that problem only recently appeared or has it been like this since installation?