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This is most important as the built in circulating pumps have magnetic drivemechanisms, which will become fouled up with iron oxide deposits circulatingaround the heating system.Failed pumps stained with brown oxide deposits or powder will not be replacedunder warranty.Schematic Plumbing Layout.The installer runs:1) A supply and return to and from the cylinder or calorifier.2) A supply and return to the heating systemBoth supply pipes have their own connection to the boiler and both returns aretwinned up and connected into one return pipe close to the boiler.When tightening up the boiler unions to the boiler, drop the front panel of theboiler to allow access to the non-return valves and hold the valve bodies witha suitable spanner to make sure that they do not rotate during the tighteningprocess.11