Given that solar thermal is an uncontrolled heat source, does one have to have any specific qualification to flush and refill a thermal system if the system is heating an open-vented (gravity) hot water system? For clarification, the primary solar water is a sealed system, but the secondary hot water is open-vented. Reason I ask is I have a customer wants the sludgy rubbishy water replaced by fresh water and solar transfer fluid. Flushing solar out seems relatively straightforward from a plumbing perspective, but I just wondered if there is are any legislative issues I need to consider? Thanks gents!