How to Replace a Central Heating Pump

The central heating pump is the beating heart of your central heating system, efficiently circulating warm water around your system to heat your radiators and keep your home comfortably warm.

But what happens if you have a problem and the central heating pump fails? If you're a competent DIYer, this is a job you can tackle yourself if you follow a few relatively simple steps. Otherwise, it’s time to call the plumber.

Why Did My Central Heating Pump Fail?

Central heating pumps fail for a variety of reasons. The most common are corrosion and a failure to flush through the system on a regular basis. If your pump isn’t circulating water round the system and the body of the pump feels hot, then you’ll need to fit a replacement.

If your existing pump has lasted for 30 years, then you may wish to replace it for a more energy-efficient model.

Choosing Your New Pump

If you’re replacing an older pump, check if it's a standard size. If not, you may need special adapters.

Measure your old pump, and make a note of the maker’s name and any settings. It may be easier to take a photo.

Choose energy-efficient central heating pumps and don’t oversize - a professional will advise you on the best replacement pump.

What You’ll Need

You’ll need to equip yourself with the following tools and equipment:

- A new pump - choose the most energy-efficient model you can afford

- A plumber's tool

- A screwdriver - use an electrical one

- A bowl or an old paint tray and some towels

- Paper and pen/your phone

First Steps

First, close down the central heating system by switching off the electricity. Never undertake a pump replacement while the current is running.

Now make a diagram of the wiring schematic so you’ll know how to connect the new pump. You could even wrap different colours of electrical tape around each wire for ease of reference and so you’re absolutely clear on what goes where. The simplest way may be to take a photo on your phone for reference.

Removing the Old Pump Unit

Now you’re ready to remove the faulty pump. First, close the service valves, which you'll find on the body of the pump, either by hand or with your plumber's tool. If no valves are present, you’ll need to drain your heating system completely.

To avoid any potential spillages, place an old paint tray or a bucket under the pump. Now locate the union nuts which hold the pump in place.

Gently turn the nuts anticlockwise (remember: left to loosen, right to tighten), and then remove the failed pump.

Replace the Pump

Ease the new pump into position, ensuring it fits snugly. Don't be tempted to re-use washers, as they can can contract over time - fit new ones in the union nuts for a watertight seal. Tighten the nuts finger-tight before finishing the job with your adjustable spanner. Now you can check for leaks by turning on the service valves or refilling the system.

Next, you’ll need to make sure the unit is bone-dry before reconnecting the wiring according to the wiring diagram you made earlier.

Testing Your New Pump

Now to get your new pump up and running. Switch the electricity back on and kick-start the heating system by turning up the thermostat.

Now you’ve got the central heating system up and running, check for any leaks or significant discharge of water. You may want to call a plumber to make sure there are no problems with the new installation.

Complete Your Installation

Finally, it's a good idea to bleed the system to make sure there's no trapped air. Your pump will have a bleed screw that you turn anticlockwise until you hear a hiss. You’ll probably need to bleed the radiators as well to ensure the whole system is balanced.

Bleeding the system will help to safeguard against corrosion and protect your newly installed pump.

Maintaining Your Central Heating System

It’s a good idea to flush your system through occasionally and to add a descaler and a rust inhibitor to it. Some descalers need neutralizing before an inhibitor is added, and you should always add the same inhibitor as is already in the system. Check the manufacturer’s instructions.

Make sure your central heating system is serviced by a qualified professional on a yearly basis to keep it running efficiently.

Ask the Professionals

If you do run into problems with your central heating pump, Anchor Pumps have a comprehensive range of replacement pumps, including highly rated energy-efficient Grundfos pumps. Contact us for more details 0800 112 3134.

Need more information on central heating pumps? Read our complete guide here.