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Central Heating Pump Overrun [3 Main Reasons & Solutions]

It’s been just a week since you installed a central heating pump.

But suddenly, you see your pump is running even after you turn it off!

It isn’t very pleasant

Still, there are some possible causes for this.

Why is my central heating pump overrun?

First of all, this is not a very big issue! Your pump usually overruns when it has a defective thermostat and timer. Your pump would also be overrun because of problems with the boiler’s wiring. Even a damaged PCB might cause this issue!  

This is just a preview. You indeed have to know more to stop your pump from overrunning.

We have provided exactly what you need in easy words.

Let’s dive into it!

Reasons behind Central Heating Pump Being Overrun

Pump overrun should last no longer than 5 to 10 minutes. It should usually last until the heat has dissipated. You might see the pump run for more than 2 hours on end or consistently. 

There can be an issue with the system if you experience this. Plus if it runs for a long time, Grundfos central heating pump can get hot!

But don’t worry! Central heating pump overrunning is a common scenario nowadays. You have to go through these reasons and solutions-

Defective Thermostat And Timer 

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A pump overrun might be due to a defective thermostat or timer. You might not know what a thermostat or a timer is. 

Thermostats are known as thermostatic radiator valves (TRVs). It controls the temperature of individual radiators and turns them entirely off. 

You can identify a faulty thermostat with a few things-

The temperature gauge readings would be relatively high, indicating that the engine is overheating. The temperature would fluctuate irregularly too.

When a thermostat malfunctions, it becomes trapped in a closed position. The coolant circulation is obstructed. 

The engine overheats, and the boiler gets quite hot. s a result, the coolant cannot reach the radiator to cool it. The pump might produce annoying noise as well. Programming defects could also be blamed for the override of the thermostat’s directives. 

Lastly, a timer ensures your boiler turns on or off at predetermined intervals. It’s significantly beneficial, especially when you’re at work and arriving home. 

A faulty timer disrupts the time management of the boiler. This issue leads to the pump making repetitive noise as well.


What do you do now? Well, it’s no big deal! You’ll need a gas-safe registered expert to fix it. They’ll then look for any loose wires and, if necessary, replace the fuse. 

Are you confused about which is the best fuse to replace with? Relax! We’ve got two of the best fuses with desired features-

Product 1
Product 2

These have pretty good control with water pumps and many more features. You can believe these products without any hesitation!

Now, let’s learn more about how the engineer will solve the problem-

The engineer can examine the power levels from the programmer to the thermostat. They would do it by connecting the programmer to another programmable device. They would also look over the pulsing issue of the central heating pump.

In terms of defects in the programmer, there is a solution as well! It would be best if you had a safe gas engine again. They’ll do a complete inspection. 

Broken Pump Circuit Board /PCB/

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Another cause behind the pump overrun can also be a broken PCB as well. PCB is the Pump Circuit Board. It’s an electronic circuit board that controls the water pump’s pressure. 

Negative feedback loops are fundamentally present on the PCB. This device guarantees that damage to the boiler is kept to a minimum and that safety comes first.


You’ll need a gas-safe registered expert to fix this as well. The expert can identify the issue and will know how to handle it securely. 

But remember one thing! Never try to address the problem yourself. Since this could endanger your home and health. 

Boiler’s Wiring Issues

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Sometimes along with the pump, your boiler won’t turn off either. In that case, the cause could be a wiring issue.

The low-temperature switch could also be the reason for this issue. This switch keeps the boiler running if the water inside isn’t being heated adequately. 


Tampering with wires can cause electrical hazards with most appliances. We always suggest you contact a gas-safe engineer to solve the problem. Your engineer may disconnect your boiler’s power supply and inspect its wiring during the repair. 

They may even examine the shut-off temperature controls. They would pay special attention to the low-temperature switch. 

These are some reasons that can be responsible for the overrun issue of your central heating pump. We hope you get your Safe Gase engineer as quickly as there is an issue!


Is it good having a pump overrun?

Pump overrun is required in most modern heat-only boilers to remove excess heat. It also prevents water from boiling in the heat exchanger when turned off. The majority of manufacturers mitigate this danger by utilizing a pump overrun.

How do I amend the ignition lockout on a boiler?

You know your boiler is locked out when you observe a red light flashing or consistently glowing. Turn the temperature control knob entirely counter-clockwise to reset. Hold your breath until the red light turns off. Return to your previous setting.

Is the central heating pump overrunning for a while okay?

Pump overrun is a typical boiler function. Its job is to remove any residual heat so that your boiler’s components don’t get damaged. If your system has this feature, it will turn on after you’ve used the heating or hot water.