

Assuming the circulators have been installed correctly, and the electrics and controls are good, then the most common cause of failure is outlined below.
Canned rotor circulators are manufactured by all the big brands, Grundfos, Xylem, Wilo, and plenty of others. The major advantages of this design are that they are very quiet in operation because they have no cooling fans and can be more compact.
However, the design also means that the pumped liquid is in close contact with the electric motor and the magnetic fields therein. Where the heating circuits are old or not treated there will be a build-up of iron (magnetite) and other dirt and particles within the motor which can eventually cause the rotor to seize.
If you are going to fit canned rotor circulators ensure the systems they are in are clean to begin with, and regularly treated with inhibitors to prolong the life of the system.
If you have doubts about the how clean the system is, or that it won’t be properly looked after, then fitting a glanded circulator that has fan ventilated motors, not the canned rotor variety, will alleviate this cause of failure. And of course, they are also available with variable speed drives to maximise efficiency.
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