Extract from 'Central Heating - Fault Finding & Repair'

Introduction
Circulating pumps should give many years of quiet efficient hot water circulation. They are precision manufactured to a high quality standard and are robust and resistant to corrosion. They may overheat if covered with insulation or linen and may seize if the system water contains corrosive particles of rust and sludge.
After long periods of non-operation (the summer months) rust and sludge sediment may settle within the body which cause the pump to seize when first started. Therefore, before the pump is started it is good practice to remove the vent plug and rotate the shaft using a small screwdriver. Continue to spin the shaft until it runs freely, replace the vent plug, set the speed to maximum and turn on the system. After approximately 30 minutes reset the speed selector to its original position.

Circulating Pump Overhaul
Most modern pumps can be overhauled for cleaning etc.
1. Turn off the boiler
2. Turn off the electrical supply to the boiler and pump, remove plug(s), fuse(s) and put them in your pocket,     etc
3. Remove circulating pump terminal cover
4. Caution - using a multimeter check the voltage at the pump     terminals. There should be a zero reading
5. Close the isolating valves on either side of the circulating pump     or drain boiler
6. Unscrew the four bolts holding the pump head to its base using     a 4mm hexagonal ‘T’ bar
7. Carefully pull the circulating pump head forward. Mop up water     spills
8. If the water is red or black or contains debris the whole
    central heating system must be flushed and protected
9. Carefully place a flat-head screwdriver between the bearing     plate and rubber gasket. Do not try to lever off the impeller
10. Carefully lever around the circumference between the bearing plate and the rubber gasket. This willwithdraw       the rotor can and the rotor/impeller assembly
11. Tap the end of the rotor shaft to remove the rotor/impeller assembly from the rotor can
12. Completely remove the rotor/impeller assembly
13. Using a detergent mixture clean the rotor and shaft and the inside of the rotor can
14. Rinse thoroughly. (Protect electrical components from water)

Re-Assembly
1. Refit the rotor can into the motor head. Ensure the rubber upper sealing ring is in place at the top of the can
2. Fit the lower rubber gasket onto the rotor can and lightly position the rotor assembly into the rotor can
3. Re-fit the head to the pump base and hand tighten the four bolts
4. Fully tighten the four bolts in turn diagonally a little at a time, this will pull the assembly into position
5. Check the rotor movement, using a 3mm screwdriver place
    the end of the slot of the rotor. Make sure it moves freely
6. Open the isolation valves
7. Replace the vent plug
8. Replace terminal cover
9. Set the speed selector to maximum (three)
10. Replace any fuses and turn on the electrical supply.
11. Set the room thermostat to maximum
12. Set the programmer to central heating ‘on’
13. Turn on the boiler
14. Adjust pump speed
15. Reset room thermostat to original setting

Extract from 'Central Heating - Fault Finding & Repair'