The circulation pump in a boiler-equipped heating system moves the water around inside its circuits. The pump pushes or pulls the freshly heated water from the boiler and sends it to the tank, if one is fitted, then around all the pipes and heating devices -- usually radiators -- and lastly pushes or pulls it back through the boiler to be heated again. Noise from the circulation pump is a sure indication of an issue that must be addressed.
Unrelated problems can be misdiagnosed as issues with the pump. If the only symptom is that the radiators do not heat up, ensure there is heated water in the boiler and the tank, if one is fitted. If the water is cool, the thermostat or the heating elements could have failed or the fuel source could have been interrupted. Many pumps have a relay on them that is activated by a small wire from the thermostat and use a heavier, 120-volt wire as their power supply; use a multimeter to check that the relay is functioning. Check that there is electricity to the circulation pump. Only if there is noise coming from the pump when it is operating should it be the first component checked.
Circulation pumps should be all but silent in operation. The most common cause of a chattering noise is air trapped inside the pump housing; follow the manufacturer’s instructions to bleed the pump. If, after bleeding, the noise persists, the issue is mechanical. A worn bearing is the most common cause, but shattered impellers -- sometimes called veins -- are not unknown. The pump must be removed before further diagnosis can take place.
Pumps are seldom hard-wired; rather, they are powered through a cord that is plugged into an outlet. Unplug the cord to ensure that power is not available at the pump. Switch the boiler to “Off,” and move the thermostat to its lowest position as a safeguard. Drain the water system; locate the drain plug and empty the water. Place a drain pan or some old towels under the pump, because some leakage from the system is still to be expected. Use a properly sized wrench if available, or an adjustable crescent wrench if one is not, to rotate the nuts counterclockwise that hold the pipes to the pump. Support the pump with your free hand so that the force is not transferred to the pipes.
Shake the removed pump. If you hear a rattling from inside, this confirms that either a bearing is worn or the impeller is damaged. Replacement is invariably cheaper than repair. Pumps are available from plumbers’ merchants and from most home improvement warehouses. Ensure the replacement has exactly the same pipe-to-pipe dimensions, and that the mounting bracket fastenings match. If no rattling can be heard, ask the help desk at a plumber’s supplier to diagnose the fault.
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