Paul Wilson
Depends. Few things can be wrong. The inlet pipe to fill system has restricted parts inside, these are designed to be left alone if water is from a main supply to help reduce the water pressure. If you are gravity these should all be remove to have a full flow. Other issue could be the older system has a part that allows water to pass through either the size of a needle hole (mains ) or bigger for gravity. Some traders don’t swap even if supplied.
