yes check the worcester website
http://www.worcester-bosch.co.uk/installer/products/gas-boilers/greenstar-highflow-440cdi/optional-plug-in-controls.
Remember though that the boiler is essentially a combi, it just has a hot water store. if you do fit a timer then you will need to wait longer for the water to get hot at the tap, and it will still warm the store to some extent, so it may be a bit of a watse of money.
Ian, August 2009