Technical Info - Replacing

Extract from 'Central Heating - Fault Finding & Repair'

There are six steps to replacing a domestic circulating pump, each as important as the other. Perhaps the first step should be to consider upgrading to an automatic and fixed speed circulating pump. If one step is not carried out correctly or is overlooked there are a number of system and/or circulating pump problems that may arise.

a) Removing the old circulating pump
b) Flushing and protecting the system
c) Circulating pump location, siting and position
d) Fitting the new circulating pump
e) Venting
f) Setting the speed

Removing the Old Circulating Pump
When replacing an old circulating pump there will be water spillage so be prepared to protect flooring etc and have a bowl and old towels/rags to mop up.

1. Turn off the boiler
2. Turn off the electrical supply to the boiler and pump, remove plug(s) put fuses in your pocket etc.
3. Remove the circulating pump terminal cover
4. Caution - using a multi-meter check the voltage at the pump terminals. There should be a zero reading.
5. Note (write it down!) the colour of each wire and its corresponding terminal letter or number
    Brown (or red) - Live to Terminal L or 1
    Blue (or black) - Neutral to Terminal N or 2
    Green/Yellow (or green) - earth to Terminal E or 3
6. Note (write it down!) the way the pump is installed
7. Note (write it down!) the water flow direction. This is indicated by an arrow on the pump often cast into
    the base of the pump
8. Remove each electric wire from its terminal
9. Turn off the isolating valves fitted either side of the circulating pump by turning the slot through 90° or
    by closing down (turn clockwise) the wheel operated gate valves
    If isolating valves are not fitted the system must be drained.
    Alternatively, the pipe work on either side of the pump can be frozen. This will allow the pump to be removed     and replaced and isolating valves can be fitted allowing for future pump maintenance
10. Remove the vent plug and deal with any water spillage. Note the colour of the water. If it is clear with
      no debris the system water does not need to be changed. If it is dirty (a reddish or blackish colour) or
      contains debris the system must be flushed and protected
11. Hold the circulating pump in one hand to steady it, loosen the union nut between the isolating valve and
      pump with a pipe wrench, pliers or large spanner
12. Repeat 11 on the other union nut
13. Holding the pump, completely undo both union nuts
14. Remove the circulating pump

Flushing and Protecting the System
It is essential to minimise the possibility of future damage or inefficient operation by ensuring the whole system is clean and protected against corrosion.

Circulating Pump Location, Siting and Position
Before installing the new circulating pump be aware that position and siting within the system is important.

Also, of great importance is the pump installation position. When installed in vertical pipe work it should pump upwards. This will ensure the circulation pump shaft is horizontal which reduces the thrust bearing load. Further this will remove air from the rotor chamber and impeller housing.

If it is unavoidable the circulating pump may pump downwards but only when an air purger and air vent is built into the system just before the pump. This will prevent air locking of the circulating pump. However, the air vent itself can allow air to enter the system so downward venting pumping should be avoided if possible.
In horizontal pipe work it is essential that the circulating pump shaft is either horizontal or slightly higher at the vent plug end by 2–5°. Do not install with the shaft below the horizontal plane as this will cause premature wear and tear of the top bearing and shaft, quickly leading to pump failure. Do not install the circulating pump with the shaft in the vertical plane as this will cause noise and premature wear and tear of the top bearing and shaft leading to circulating pump failure. However, with a sealed system pressurised to a minimum of 1.5 bar if there is no other option the shaft can be in the vertical plane.

Fitting the New Pump
Circulating pumps can be replaced either on a like for like basis, if available, or leading manufacturers provide replacement guides and fitting kits/recommendations for using their pumps. This is also an opportunity to upgrade to an automatic and fixed speed circulating pump (see Pumps – 9.2). An example is shown below:

1. If fitting a different make pump follow the manufacturers recommendations for any pipe work adjustment or     the use of fitting kits
2. Remove the old gaskets from the isolating valves and clean the surfaces. Do not use the old gaskets
3. Do not apply sealants or jointing compounds to any surface including the threads of the isolating valves or     the pump port threads. Assemble dry
4. With the flow arrow in the correct direction (check your notes) place the new circulating pump into position     between the isolating valves
5. Slide the new gaskets into place
6. Hand tighten both union nuts ensuring the gaskets do not move out of position
7. Steady the new circulating pump with one hand and tighten both union nuts. Do not over tighten. Ensure
    the pump is at the correct angles
8. Open the isolating valves
9. Important – vent the circulating pump
10. Remove the terminal cover and using your notes rewire the new circulating pump
11. Replace the terminal cover
12. Set the speed selector to maximum (three)
13. Replace any fuses and turn on the electrical supply
14. Set the room thermostat to maximum
15. Set the programmer to central heating ‘on’
16. Turn on the boiler
17. Adjust pump speed

Extract from 'Central Heating - Fault Finding & Repair'


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