It may be there is a low (water pressure) ballvalve in the downstairs loo. This is usually the case for tank fed loo's, but obviously yours is mains fed, so the error could be there? Check and compare the fill rates (by eye) on both loo's and that could be the answer.
As well as that it may be the stop tap for the house is not fully opened check both the inside and outside stoptaps. Another cause is you may be in a low water pressure area or more than likely a combination of all of these diagnostics. If the downstairs loo does have a low pressure ballvalve than you can change it for a high pressure following the instructions given on the following link. (you will have to search the site. 'replacing ball valve' is a good query) good luck... dont drown. http://www.ultimatehandyman.co.uk
The drip., December 2010
