If you’ve ever wondered about the mysterious-sounding term “boiler pump overrun,” you’re not alone. Many homeowners encounter this term when dealing with their heating systems but might not fully understand what it entails. Don’t worry; we’re here to shed some light on the subject and help you grasp the concept.

What is a Boiler Pump Overrun?

Boiler pump overrun is a feature found in many modern heating systems, particularly in combination (combi) boilers. It refers to the continued operation of the boiler pump for a brief period after the boiler has stopped heating your home. This might seem counterintuitive at first, but there’s a good reason for it.

Why Does It Happen?

The main purpose of boiler pump overrun is to ensure that the heat generated during the heating cycle is distributed efficiently throughout your home. When the boiler stops producing hot water for heating, the residual heat in the boiler’s heat exchanger is still available to warm up your radiators or underfloor heating system. The pump continues to circulate water through these systems, making the most of the remaining warmth.

What’s Causing Your Boiler to Be in Constant Overrun?

Boiler pump overrun is a common and useful feature in many heating systems, but if you find that your boiler is in constant overrun, it may indicate an issue that needs attention. Let’s explore some possible causes for this situation:

1. Faulty Thermostat

A malfunctioning thermostat is a common culprit for constant boiler pump overrun. If the thermostat fails to communicate the desired temperature accurately, your heating system may continue to run even when it’s not needed.

Solution: Have your thermostat checked or replaced by a qualified heating engineer.

2. Incorrect Boiler Settings

Sometimes, the settings on your boiler might be incorrectly configured. This could result in the boiler running longer than necessary.

Solution: Review your boiler settings or consult a professional to ensure they are correctly adjusted.

3. Pump Issues

If the pump in your heating system is malfunctioning or blocked, it can cause the boiler to remain in overrun.

Solution: Contact a heating engineer to inspect and repair or replace the pump if necessary.

4. Boiler Sizing

If your boiler is oversized for your heating needs, it may frequently go into overrun as it produces more heat than your home requires.

Solution: Consult a heating engineer to assess whether your boiler is appropriately sized for your property.

How to Fix a Central Heating Pump Overrun

If you’re experiencing a central heating pump overrun issue, it’s important to address it promptly to ensure energy efficiency and prevent unnecessary wear and tear on your system. 

Here are steps to fix it:

1. Check Thermostat Settings

Ensure your thermostat is set to the desired temperature and is functioning correctly. If it’s outdated or malfunctioning, consider replacing it with a modern programmable thermostat.

2. Boiler Settings Review

Inspect your boiler’s settings and timers. Make sure they are adjusted according to your heating needs and schedule.

3. Pump Inspection

Have a heating engineer inspect your central heating pump. They will check for blockages, wear and tear, and ensure it’s functioning optimally.

4. Consider Boiler Replacement

If your boiler is old and frequently goes into overrun, it might be more cost-effective in the long run to invest in a new, energy-efficient boiler.

5. Regular Maintenance

To prevent future issues, schedule regular maintenance for your heating system. Annual servicing can identify and address problems before they become major concerns.

Remember, if you’re unsure about any of these steps or if the problem persists, it’s best to consult with a professional heating engineer from MCR GAS. They can diagnose the issue accurately and provide the necessary solutions to ensure your heating system operates efficiently.

When Does It End?

The duration of boiler pump overrun can vary depending on the specific boiler and heating system. Typically, it lasts anywhere from a few minutes to around 10 minutes. Once the residual heat is fully utilised, the pump stops, and your heating system enters standby mode until the next heating cycle.

Should You Be Concerned?

In most cases, there’s no need to worry about boiler pump overrun. It’s a normal part of how modern heating systems operate. However, if you notice unusually long overrun times or other heating issues, it’s advisable to contact a professional heating engineer to inspect and service your boiler.


Boiler pump overrun might sound technical, but it’s a simple yet effective feature designed to make your heating system more efficient and your home more comfortable. If you have further questions or concerns about your boiler or heating system, don’t hesitate to reach out to the experts at MCR GAS. We’re here to provide useful information and solutions for all your boiler-related issues.

Remember, a well-maintained heating system is the key to a cosy and warm home during those chilly months. Stay comfortable, stay informed, and trust MCR GAS for all your heating needs.

Visit MCR GAS for more heating tips and services.