We have a loud whooshing noise when the hot water tap is turned on downstairs and up stairs , it's not coming from the boiler , but from above the kitchen , it's been getting worse , had a plumber round and he thinks it is an isolation valve not fully opened in the ceiling somewhere ? Had a major refurb on the house over a year ago no issues then , but did have a leak on my mains line outside recently could some grit get into the system ? Can it be anything else ? We are in a hard water area could it be build up in the pipes ? Can it be cleaned ? Any ideas would be great .