How to fix heating boiler circulating pump mounting flanges

Updated February 21, 2017

One of the most common places for boiler leaks to occur is at the circulation pumps. These are the pumps that supply hot water to the radiators throughout your home or office building. A leaking circulation pump can mean that the mounting flanges need to be replaced. This is evident by large amounts of corrosion or just simply water dripping from the bottom or top of the circulation pump. Fortunately, this is a simple fix.

Turn the heat off at the thermostat and turn the breaker off to the circulation pump. Turn the water shutoff valves to the closed position above and below the circulation pump on the water line.

Open the wire housing box and disconnect the wires to the circulation pump motor. If the wires do not correspond by colour, mark the wire that goes to the black (hot) wire on the pump with a piece of electrical tape, and the wire that goes to the white (neutral) wire with two pieces of electrical tape. A bare wire or green wire is always the ground wire and should be easily identifiable. Screw the wire nut over the wires that run to the boiler disconnect or breaker panel.

Remove the bolts on the top and bottom flanges with a socket wrench. Keep the bolts in the flange holes for stability. Remove the pump carefully and clean off any corrosion from the exterior of the pump mounting flanges with a brass brush.

Remove the mounting flanges from the upper and lower pipes with a pipe wrench being careful not to twist the pipe itself. Getting the flange to turn will be hard at first because of the pipe dope that was originally used to seal the flange. Coat the inside of the new mounting flanges with pipe dope and turn them onto the pipes by hand as far as possible, then use the pipe wrench to finish threading them onto the pipes.

Install the circulation pump by mounting it to the new mounting flanges. Insert the bolts and tighten down the pump to the flanges. Adjust the flanges as necessary. Test your work by turning the water shutoff valves to open. Inspect for any leaks.

Rewire the circulation pump, making sure that the wires are secure inside the wire nuts. Close the circulation motor and wire cover and turn the power back on to the pump. Turn on the thermostat to heat and turn up to test. It may take a few minutes for the boiler to heat the water up enough for the circulation pump to turn on.


Hold onto the pipe with one hand while turning the mounting flanges so you do not break the pipe or the solder down the line of the pipe.


Wait until the temperature outside is warm enough to not need heat from the boiler in case of issues with repair or further mechanical issues that arise from unrelated repairs or equipment. Never disassemble piping shortly after heating system use as the water temperature can reach 82.2 degrees Celsius. Use caution when working on hot water and steam systems at all times.

Things You'll Need

  • Pipe wrench
  • Pipe dope
  • Small socket set
  • Brass wire brush
  • New circulation pump flanges
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About the Author

Adam Yeomans has been writing professionally since 2010, with his work appearing on websites such as eHow. He works in the construction industry as a builder and as an energy efficiency consultant.