Boiler Pump Not Working: Causes and fixes explained

If there’s an issue with your boiler pump, you may be lost as to what to do.

If you’re wondering whether you can fix it DIY or if you must hire a professional, you’ve come to the right place.

This guide will look at the main causes and fixes when a boiler pump isn’t working.

Let's get pumpin'

What Exactly is a Boiler Pump?

A boiler pump (a.k.a. circulatory pump or central heat pump) is designed to pump hot water around a central heating system. 

This way hot water can reach your radiators to heat your home before returning to your boiler to be reheated at a later point.

Modern boiler pumps are not just effective at their job but are geared towards increasing efficiency.

Of course, some of the hot water will be pumped towards appliances like showers and taps for direct hot water use.

Can I Fix a Boiler Pump DIY?

This would depend on the nature of the issue and the level of your skills and knowledge related to the work required.

Generally, it is actually okay for a DIY'er to replace a boiler bump so long as they take all of the necessary safety steps and know exactly what they are doing.

If in doubt, always hire a qualified heating engineer.

Causes and Fixes for a Malfunctioning Boiler Pump

Of course, the nature of boiler pump issues can vary a lot.

What’s more, there are several potential fixes for each cause of a malfunctioning boiler pump.

Some of these fixes may be DIY-friendly, while others aren’t.

The pump Won’t Circulate Water

One of the more common issues a boiler pump can experience is that it loses the ability to circulate water.

This tends to be the result of a propeller inside the pump that has seized.

When this happens, a seized propeller usually accompanies the boiler pump giving off a vibrating sound. Another possibility is that there’s a problem with the motor. 

Potential Fixes:

• Freeing seized components
  If your boiler pump is working fine in most regards but there are one or more seized parts, you may be able to fix it by giving the pump a gentle tap. This should free any seized parts.

• Replacing a boiler pump
  When a professional is needed: If components continue to seize on recurringly, this means it’s time to have your boiler pump replaced.*

*We discuss the details of how to replace a boiler pump toward the end of this article.

Lack of Power to the Circulator Pump

A less common issue involves the boiler pump and only the boiler pump failing to receive power.

You’ll know if this is the case if all other electrical appliances are functioning correctly, but your pump isn’t working.

This is likely the result of faulty wiring or a malfunctioning PCB. 

The PCB or Printed Circuit Board is basically the control centre of your boiler that keeps everything running smoothly and monitors all components to ensure there are no issues.

Whether the issue lies with your PCB or wiring, you must hire a qualified heating engineer to fix this problem.

Unlike freeing seized components or replacing a boiler, all of these fixes must be dealt with by a professional.

Potential Fixes:

• Fixing or replacing a PCB
  It’s possible that PCB can be fixed if there’s a small fault, but it may very well need to be replaced. Either way, this work can only be undertaken by a Gas Safe Register engineer.

• Fixing faulty wiring
  If the wiring connecting the boiler pump and PCB is faulty, then a professional will need to fix this to get your pump back in working order.

Leaking Boiler Pump

Another possible issue that you may face is a leaking boiler pump.

There are several potential causes for this, including corrosion, a loose boiler pump, and blown seals.

If you know what you’re doing, you could inspect the pump yourself in an attempt to pinpoint the issue.

Here’s what you should check:

• Whether the pump is securely fastened.

• Ensure the boiler pump’s seals have not blown.

• Inspect the pump to see if there’s any evidence of corrosion.

Potential Fixes:

• The pump needs tightening
  You may notice that the pump isn’t fastened securely. If this is the case, you could try tightening it yourself. This should get your boiler pump working again.

• Replacing seals
  If the seals are blown, a qualified heating engineer will be required to replace them. However, if the boiler pump is particularly old or has been faulty on many occasions before, it may best to simply have the entire boiler pump replaced.

• Replacing the boiler pump
  Aside from being a potential solution to blown seals, if you notice any evidence of corrosion on the boiler pump, it will definitely need to be replaced regardless. Again, replacing a boiler pump is DIY-friendly so long as you take the required safety steps and have the necessary skills and knowledge. Otherwise, hire a Gas Safe Register engineer.

Boiler Pump Is Making Noise

You may notice unusual sounds coming from your boiler’s circulatory pump.

This could be a sign of an airlock in the pump.

This is especially likely if the pump is producing unusual noises and your boiler is also locking out.

Potential Fixes:

• Releasing trapped air
  Thankfully this issue can usually be fixed using a DIY-friendly solution. If you’re confident that there’s an airlock in the boiler pump, check to see if it comes with a bleed screw. If there isn’t one, you’ll need to hire a professional. However, if it does feature a bleed screw, you can turn it a little to release the trapped air. As soon as the hissing comes to an end and a small quantity of water emerges, it’s time to close the bleed screw again. The problem should now be solved.

• Hiring a professional
  Again, if there is no bleed screw or the boiler is producing unusual sounds but isn’t locking out, hire a heating engineer to take a look.

Boiler Pump Won’t Turn Off

Lastly, while it’s unlikely, you may find that your boiler pump is failing to turn off.

Should this be the case, you must hire a professional to take a look.

From there, the heating engineer can inspect your boiler and its pump, diagnose the issue, and hopefully fix it there and then.

A repair job or replacement work may be needed.

Potential Fixes:

• Faulty PCB
  In this case, either the PCB will need to be fixed or perhaps even entirely replaced. *

• Pump overrun stat malfunction

• Mid-position valve is stuck in place

*If a component as expensive as your PCB needs to be replaced, it may be more financially sensible to have your boiler replaced. This is because a PCB replacement usually costs around £500 to £800. Given the cost-of-living crisis, however, many households would consider it impractical to replace their boiler right now. But the good news is that it’s possible to purchase a boiler on finance and in some cases even with zero interest.

Cost of Fixing or Replacing a Boiler Pump

So, what are the costs of the various potential fixes laid out in the previous section? Of course, for jobs that can be undertaken DIY or by a professional, the cost would depend on who you hire. 

Also, for DIY fixes, naturally, these do not come with the cost of labour.

Please be aware that you should only attempt DIY fixes if you are sure that these solutions are appropriate (as per the prior section).

If in any doubt, always hire a professional.

DIY Solutions

• Replacing a boiler pump
  £90 to £200

• Freeing seized boiler components
  No cost

• Pump needs tightening
  No cost

• Releasing trapped air
  No cost

Hiring a Professional

• Replacing a boiler pump
  £150 to £380

• Fixing a PCB
  £60 to £240

• Replacing a PCB
  £490 to £800

• Fixing faulty wiring
  £60 to £180

• Pump needs tightening
  £30 to £120

• Replacing seals
  £50 to £220

• Releasing trapped air
  £30 to £60

• Inspecting and fixing a boiler that is producing noise
  £30 to £240 *

• Repairing a pump overrun stat malfunction
  £30 to £120

• Fixing a mid-position valve that is stuck in place
  £30 to £120

*This price can vary greatly as it would depend on the nature of the problem.

How to Replace a Boiler Pump

As mentioned earlier, you should only remove and replace a boiler circulatory pump if you are confident in your skills and knowledge to undertake this work.

If in any doubt, always hire a Gas Safe Register engineer.

Please note that you should follow the instructions given by the boiler pump manufacturer(s) as to how you should remove the old pump and what steps are needed to install the new one.

The steps described below are a summarization of what’s involved.

1. Purchase the Correct Replacement

Before you replace a boiler pump, it’s critical that you buy the right boiler pump.

If you end up purchasing the wrong one, you’d end up wasting money, or worse causing damage to your boiler in an effort to fit the new one.

So, make absolutely sure you get the right one for your boiler. Consult a professional or renowned manufacturer if you have any concerns.

2. Turn Off the Power and Disconnecting Wiring

First things first, you must isolate the power at the mains before engaging in any of the following work.

This is essential for your safety. After all, electric shocks can prove deadly.

Once you’ve definitely isolated the power at the mains, locate the electrical connection cover on your boiler pump.

Carefully take it off before removing the wires from the live, neutral, and earth positions.

You may want to take a picture with your phone, so you don’t forget which wire goes where!

Once you’ve removed these wires, you can unclamp the connection box cable and remove it clear of the boiler pump.

3. Turn the Inlet and Outlet Valves to their Off Positions

Next, find the inlet and outlet valves. You can turn these to the off positions by turning each clockwise with an adjustable spanner.

If any of the valves are jammed or otherwise won’t move, you should hire a professional as additional steps are likely required.

4. Disconnect and Remove the Existing Pump

You can now remove the old boiler pump. To do this, you need to undertake the following steps:

• Remove the nuts that connect the boiler pump to the pipework. You can do this with a Stilson wrench. Make sure you do not interfere with the connection that combines the pipework to the opposite side of the valves. Otherwise, leakage may result.

• You should also put some rags or a paint roller tray beneath the pump since a certain amount of water will drip out.

• Once everything is disconnected, the existing pump is ready to be fully removed.

5. Install the New Boiler Pump

Once you’ve removed the old pump, you can fit the new boiler pump into place.

Don’t forget to confirm that you installed the boiler pump in the right direction.

There is usually an arrow on a boiler pump to show which way the water travels.

If in doubt, double-check again with the manual or consult a professional.

Also, the washers should be replaced with new washers.

Next, tighten the inlet and outlet valve connection nuts.

You should do this by hand at first to ensure they are tight while also ensuring that they do not cross-thread.

Once you verify this, then you can use a wrench to tighten them further. However, you shouldn’t over-tighten as this could harm the threads.

6. Re-connect the Wires and Test Your Boiler Pump

Once you’ve fully installed the new boiler pump (and again ensuring that the power is still isolated at the mains), remove the connection box cover for the electrics of your boiler bump. 

Wipe the connection openings gently with a light cloth to ensure there is no moisture.

Then reconnect the wires that you disconnected earlier (i.e., live, neutral, and earth cables) in the right positions.

Check the image you took on your phone from earlier if you decided to take this approach.

Put the connection box cover back in place. Use the thermostat in your room to put the temperature up.

Once you’re sure that everything is correctly in position, turn the power back on at the mains.

Now you can turn the heating on itself and hopefully, that should get the new pump working in no time.

In many cases, you should hear the new pump kicking into action as it first pumps water through your central heating system.

If not, check the manual for more information or consult a qualified heating engineer.

7. Bleed Air from the New Boiler Pump

Lastly, you’ll need to bleed air out of the newly installed boiler pump. Gently open the bleed screw until you notice a hissing noise.

Wait till the hissing stops before closing it shut again.

As the hissing comes to a halt, a little bit of water may come out of the bleed valve so you may want to have some rags fitted beneath the pump in case this happens.

Lastly, you may also find it’s necessary to bleed your radiators since the boiler pump (as a result of being newly installed) may have pumped air throughout your heating system.

You’ll have a sense that your radiators need bleeding if you notice they have dropped in efficiency/effectiveness or if there are cold spots on your radiators.

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