help needed-fuelsaver mk2 boiler+potterton ep2002 programmer

I live in a shared, rented, house. Landlord useless. We know nothing about plumbing or electrics. We cannot have the heating switched on without the hot water on at the same time ( the light on the ep2002 for heat comes on and the pilot is always lit, but it won't 'fire' up until we put the H/W on also). is this a fault with the program or boiler, or just a feature of existing system?
Also, our gas and electric bills are unusually high and we wondered if this could be connected to above issue?
many thanks for any insights you may have
Lisa

the boiler is the Glowworm fuelsaver mk2 btw
we just want to be able to choose when we have hot water rather than Having to use it when we just want the heating on
thanks
lisa

if boiler works fine with heating it will be your set up or fault in system. Is it fully pumped with a motorised valve in airing cupboard, box like thing with 3 pipes on it!, or 2 x 2 port valves, one pipe either end!

It's likely to be just the way it's plumbed - which is what the chap above me said, using different words...

Make sure your electric immersion heater, assuming you have one, is turned OFF. Gas will heat it more cheaply.
Look for a thick wire coming off the round plastic or metal can on top (usually) of the cylinder.