I have an upstairs shower room which is suplied by a combi boiler. When having a shower if one of the other family members turns on the tap downstairs or even worse flushes the toilet the shower comes to a stop. I'm in the process of having a large extension which will include an extra shower room off a new bedroom. What can I do to stop or reduce this problem. My water pressure seems to be fine. Any help would be great as I have six children (Five girls and a boy) who very soon will be wanting showers at the same time.