Sweden-based Rettig ICC sells its heating products in the United States under the Myson name. Myson's CP53 is a small water pump designed to circulate hot water through a residential radiant heating system. Like any electric motor, the CP53 will fail with regular use. This particular model seems to have been prone to capacitor failure, which prevents the motor from getting the quick burst of electricity it needs on start up. Fortunately, you can replace the pump, usually for under £65 (as of March 2011).
Shut off power to the pump, then mark on a piece of scrap paper which colour wires are plugged into which sockets on the boiler's control panel. Pull the wires free from the control panel, but do not touch any exposed wires leading in or out of the capacitor on the side of the motor. Even when the power is off, the capacitor can still hold a charge.
Shut off the valves on either side of the motor by turning counterclockwise by hand.
Place the jaws of the money wrench over a nut on one end of the pump. Roll the adjustment wheel until the jaws fit securely against two flat sides of the nut. Loosen the nut until it moves freely by hand. Continue turning the nut until it slides up the pipe and away from the pump.
Repeat Step 3 for the second nut at the other end of the pump.
Pull the CP53 out of the water line and replace it with the new pump. Ensure that the water flow indicator on the pump is pointing away from the boiler and toward your system's radiators.
Wrap silicon plumber's tape around both threaded ends of the water line two times, then tighten the nuts with the monkey wrench by following Step 3 in reverse.
Open the water valves at either end of the pump by turning them clockwise, then restore power to the system.