managed to get the part yesterday! at a whopping cost of £4.12, 
heating engineer due out this afternoon to fix,ive had no heating or hot water for over 2 weeks so fingers crossed
i got the part from ideal after disputing it didnt come with the valve telling them the part number from internet,they didnt list it as one of their spares but do sell it.
they were insisting i had to buy a valve from them,but i persevered and made them see i was right.
thanks for help guys
heating engineer due out this afternoon to fix,ive had no heating or hot water for over 2 weeks so fingers crossedi got the part from ideal after disputing it didnt come with the valve telling them the part number from internet,they didnt list it as one of their spares but do sell it.
they were insisting i had to buy a valve from them,but i persevered and made them see i was right.
thanks for help guys