Homeowners Professionals

How does a central heating pump work?

You may never have considered how your heating system actually works - you turn the heating on and your radiators get hot. But there are a lot of mechanisms that work together to ensure your home stays warm throughout the winter. One such device is a central heating pump.

What is a central heating pump?

A central heating pump in a conventional boiler system pushes water that’s been heated by the boiler through your home’s radiators, taps and showerheads. Without this device, the hot water wouldn’t go anywhere. It’s usually located in or near the boiler or the airing cupboard.

The heated water gradually cools down as it moves around the system. The pump delivers the water back to the boiler where it can be reheated.

The pump works by pressurising the water with impellers and delivering this around the system. Your pump will have a water flow inlet and an outlet. The inlet is where the hot water enters to be pressurised and the outlet is where the water exits to flow around your home. The diameter of the inlet and outlet will determine the flow rate of the water.

Depending on the kind of pump you have, there may be a pressure dial so that you can increase or decrease the pressure of the water in your central heating system. It’s not advised that you adjust these all the time - it’s better to find a setting and stick to it. The dial is there so that the pump can be installed into any size home with any number of radiators. The pressure is increased for large homes and decreased for smaller properties.

If your pump is set at a pressure that’s too high, you may notice that your electricity bill is very high or that there’s a lot of noise coming from the pump. If the pump pressure is too low, you may find that your radiators aren’t heating up properly or your boiler is frequently overheating. Most pumps come with three settings so you can determine which pressure is best for you. Keep in mind that setting your pump to the highest pressure won’t necessarily heat your radiators up more quickly.

Your pump should last for between 10 and 20 years, so there’s no need to change it unless you find it’s making a lot of noise or your radiators aren’t being heated up properly. If you notice either of these things, you should call a suitably qualified engineer to have a look at the pump.

  What is a wet rotor pump?

As a pump propels the water around your heating system, it can begin to get quite hot. This is because it’s working hard to use a rotor to pressurise the water. In a wet rotor pump, the rotor is surrounded by water. This allows the motor to remain lubricated and cool while it’s running. There are lots of benefits to having a wet rotor pump. It runs very quietly so you can hardly hear it and it provides a more consistent pressure in your radiators and pipes.  

Does a combi need a central heating pump?

A  combi boiler  doesn’t need a pump for your hot water. This is because the hot water that is supplied to your taps and showers is at mains pressure. This usually means that, if your area has  low mains pressure, it’s advised that you have a conventional boiler instead of a combi.

Equally, a combi boiler doesn’t need an external pump to heat the radiators as the boiler has a pump that does this internally.  

Does this mean you can’t have a power shower with a combi boiler?

Combi boilers don’t require a hot water cylinder, as all the water is heated within the boiler itself as and when it’s needed. But a shower pump needs to be connected to a hot water tank, which is why you might not be able to add a pump to a combi system.

You should find that the pressure from your combi boiler is good enough anyway.

How to bleed a central heating pump

First, you need to identify whether your pump does need bleeding or whether there’s another issue. If your pump is showing signs of the following, then it’s likely that you do need to remove a build up of air:

  • Your pump is making a loud noise
  • Your radiators aren’t getting as hot as they should be
  • Your pump is hot to touch

All pumps will make a slight noise, so it’s only if the noise escalates to a loud banging that you should get worried. This noise is likely caused by air that’s trapped inside the pump. Pumps will also be warm to touch, so only bleed the system if your pump is very hot.

So how do you bleed the system once you’ve determined there’s a problem?

Firstly, you should turn off all the power to the pump, including at the fuse box. Don’t bleed the system when the pump is hot as there could be scalding water in there. You should lay some towels down on the floor and the surrounding area to protect the floor and any other electrics near the pump.

Next, you should turn off the water supply to your home. It is a good idea to check with your family members or roommates before you do this. Then, you need to shut off the water to your pump. There will be two gate valves located either side of the pump. Turn these clockwise until tight.

Once the water and electricity to the pump has been isolated, you can remove the bleed screw with a screwdriver. This is usually situated on the front of the pump. Take the screw out completely and keep it in a safe place.

Then, mop up all of the water that has come out of the pump and replace the bleed screw using your screwdriver.

Now, you can turn the electricity and the water back on. Remember to loosen the gate valves either side of the pump too.

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