My MVHR Unit Stopped Working – What Now?

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Does your house feel stuffier? Are your windows more foggy than usual? Do you smell damp? If so, your MVHR unit may have stopped working.

To determine whether it’s your MVHR, this guide will cover everything from identifying issues and diagnosing problems to fixing your MVHR to regain optimal ventilation.

Common Signs of a Failing MVHR Unit

Depending on your property type, the signs of a failing MVHR unit can be easier or harder.

For example, if you live in a flat, you’ll probably notice your MVHR has stopped working, as you won’t hear it anymore. They’re not very loud, around 21-45 db. However, it’s something you’ll notice.

On the other hand, in a house, these are usually located out of the way in a loft or a plant room. Most of the time, you’ll never hear them – even when they’re working.

There are other signs you can look for that indicates a broken MVHR unit:

  • Bad smells linger for longer (for example, cooking smells).
  • There’s a “stuffiness” in almost every room of your property.
  • You see flaking pain in the bathroom or ensuite door frames.
  • Condensation building up on the windowsills and/or see mould.
  • The tiles in your bathroom remain damp after a shower or bath for a day or longer.

These are the telltale signs that your MVHR (or MEV) unit has stopped working. Once you’ve identified this, you can diagnose the problem and start repairing/servicing the MVHR unit.

Understanding the MVHR Light Systems

Understanding the MVHR Light Systems

A lot of MVHR units have a light system. The light system can talk much about the current system’s physical state. This is usually a green, amber, and red-light system.

  • Green Light: The unit is operating normally.
  • Amber Light: There are minor issues or the need for maintenance.
  • Red Light: A solid red light signals a critical failure.

Red Light Failures

If a red light is displaying on your MVHR unit, it could mean it’s experiencing one of the following issues:

  • Extract Fan Motor Failure: The fan responsible for extracting stale air has malfunctioned.
  • Supply Fan Motor Failure: The fan that supplies fresh air has stopped working.
  • Both Fan Motors Failing: Both the extract and supply fans have failed simultaneously.
  • PCB or Motherboard Failure: The unit’s control board has encountered an error.
  • Combination of Failures: Both the motors and the PCB board may have failed.

A common culprit of red-light failures is the Nuaire MVHR Unit. Usually, when you see one of the signs mentioned above, you’ll see a red light on your Nuaire system. If you see this as a red light, you may need a Nuaire MRXBOX replacement.

Steps to Diagnose and Fix Your Nuaire MVHR Unit

Because the Nuaire MVHR unit is the most common culprit of MVHR failures, this guide is for them. However, the process for other MVHR brands is very similar.

Step 1: Locate the Serial Number

Finding the serial number on a Nuaire MVHR unit is straightforward. This is usually located on the left-hand side or underneath the unit. You’ll need this number to verify the warranty status and troubleshoot solutions from Nuaire.

If, for whatever reason, you cannot find the serial number on the unit, it may be on any documentation you received with the system. You may even be able to contact Nuaire customer support to get your serial number.

Step 2: Contact Nuaire

Once you have your serial number, you can contact your MVHR unit provider. For Nuaire customer support, you can contact them at 02920858200.

You’ll need to give them your system serial number and explain the problem when you’re on the phone. Depending on the issue, they may provide you with troubleshooting advice or recommend a technician visit.

Step 3: Technician Visit

If Nuaire recommends a technician visit, you’ll want to arrange a visit from a professional technician. However, your contact should have a good understanding of your system. For example, if you have a Nuaire MRXBOX, look for a professional in Nuaire goods.

It’s important to note that an MVHR technician’s call-out fee is between £90 and £200. The cost varies depending on the location and the complexity of the diagnosis.

Once the technician has looked at your system, they’ll give you a breakdown of the problems, letting you know what needs to be done to get your system up and running again.

Step 4: Replacement and Costs

Per your technician’s diagnosis, certain parts may need replacing on your unit. If it’s still covered under warranty (in this instance, Nuaire), contact them, as they’ll cover any costs for replacement parts needed.

You must cover the new parts and installation costs if your system isn’t under warranty. This can be quite a lot. Therefore, sometimes, it can be more cost-effective to purchase an entirely new unit. As a benchmark, a new MVHR unit costs around £1,000, and installation costs up to £1,600.

Repairing and Servicing Other MVHR Brands

Service ventilation system

While the guide above focuses on Nuaire MRXBOX and Nuaire products, it’s essential to know that the process is similar for all brands.

Here are the general steps for diagnosing and fixing other MVHR units:

  1. Identify Brand & Model: First, you need to see what brand and model your MVHR system is.
  2. Read the Systems Manual: Next, locate your manual or try to find the manual online. You can do this by typing in “(Brand Name” + “Model Name” + MVHR Manual)”. Here, you can read the troubleshooting steps.
  3. Contact Manufacturer Support: If troubleshooting fails, you must contact the manufacturer. The number can be found online or in the systems manual. Support may be able to provide extra details about the issue and help you troubleshoot the problem or suggest if a technician is needed.
  4. Schedule a Technician: If the manufacturer recommends a technician, you may need to book one. When doing this, just make sure the technician you choose specialises in the brand or model of your system.

Essential Considerations for MVHR Service/Repair

When getting MVHR service and repair, there are a few things you want to think about before, during, and after the process. This will help you get the most out of your money and, most importantly, improve the quality of your MVHR system.

  1. Regular Maintenance
    Regular maintenance is essential to prevent MVHR failures. Many issues arise from neglect, so schedule periodic checks to keep the system running smoothly.
  2. Quality of Service
    Choose technicians with proper accreditation and a good reputation. Ensure they warranty their repair work and respect your home environment.
  3. System Commissioning
    After repairs, ensure the system is appropriately commissioned (Commissioning Page link) to provide the correct amount of filtration. Improper setup can lead to inefficiencies and further problems.
  4. Cost Management
    To manage costs, limit technician visits by ensuring thorough diagnosis and repair in a single visit. Use warranty coverage where applicable to save on replacement parts.

Maintaining Your MVHR to Reduce Future Problems

To prevent any issues in the future, it’s a good idea to maintain your MVHR unit properly.

Why Regular MVHR Maintenance is Crucial

Regular maintenance ensures efficient operation, extends lifespan, and prevents common issues like blockages, component wear, system imbalances, and energy waste.

Additionally, early identification of worn parts prevents complete failures, and proper commissioning avoids ventilation issues. Regular maintenance also reduces energy consumption, saving on bills.

Key MVHR Maintenance Tasks

Key MVHR Maintenance Tasks
 - install vent axia home heat recovery ventilation system
  • Filter Maintenance: Clean filters every three to six months, dry them thoroughly, and replace them annually or as recommended.
  • Ductwork Inspection: Inspect for damage regularly and schedule a professional cleaning every few years.
  • Fan and Motor Check: Regularly check fans and motors, lubricate as needed, and listen for unusual noises.
  • Heat Exchanger Maintenance: Clean annually, inspect for wear or damage and replace if necessary.
  • Control System Verification: Verify sensor functionality and calibrate the control system to maintain desired settings.


After reading this post, you should better understand how to spot, find, and initiate an MVHR repair or service. If you can, fix these problems early on. Failing to repair your MVHR early on can result in more significant problems down the line.

Also, remember the costs behind an MVHR repair. These can be high. If they’re too high, say £600, then purchasing a new system for £1,000 may be better. It’ll last much longer and give your home much better air quality.

That being said, if you’re looking for an expert technician, our team at Cool Runnings LTD is here to help. We have extensive knowledge of the MVHR system (especially the Nuaire MRXBOX system) and are ready to help. Contact us today for a free quote or even for advice.

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