7 Signs Your MVHR, MEV or PIV System Needs Maintenance

7 Signs Your MVHR, MEV or PIV System Needs Maintenance

A home ventilation system normally operates quietly in the background, so it may not be immediately obvious when its performance begins to decline.

How can you tell if a ventilation system needs maintenance? Common warning signs include reduced airflow, persistent condensation, stale odours, unusual noise, dirty filters, unresponsive controls and error messages.

The exact maintenance requirements depend on whether your home uses Mechanical Ventilation with Heat Recovery (MVHR), Mechanical Extract Ventilation (MEV) or Positive Input Ventilation (PIV). However, changes in how the system sounds, feels or responds should not be ignored.

1. Airflow from the valves feels weaker

Reduced airflow is one of the clearest signs that a ventilation system requires attention.

An MVHR or MEV system may no longer be extracting moisture effectively from bathrooms, kitchens or utility rooms. With an MVHR system, the supply airflow entering bedrooms and living spaces may also feel weaker.

Possible causes include:

• Dirty or blocked filters
• Obstructed external terminals
• Dust around room valves
• Damaged or restricted ductwork
• Incorrect control settings
• A fault with the unit or fan

Avoid closing or adjusting commissioned air valves without guidance. Their positions may have been set to deliver a specific airflow rate in each room, and changing them can affect the balance of the system.

2. Condensation is taking longer to clear

Ventilation systems help remove or dilute moisture produced through showering, cooking, drying clothes and everyday occupancy.

If condensation remains on windows for longer than normal or a bathroom stays humid after use, the system may not be moving enough air. Check that extract valves are open, filters are clean and boost mode is operating correctly.

Condensation does not always mean the ventilation unit is faulty. Heating, insulation, moisture production and the overall condition of the property can also contribute. However, a noticeable change in performance should be investigated.

3. Rooms feel stuffy or odours linger

Persistent cooking smells, stale air or rooms feeling less fresh can indicate reduced ventilation.

An MVHR system extracts stale, moisture-laden air while supplying fresh filtered air through a separate duct network. An MEV system continuously extracts air from wet rooms, while a PIV unit introduces filtered air to encourage movement through the property.

Because these systems operate differently, the source of the problem will vary. Dirty filters may restrict an MVHR or PIV system, while an MEV system may be affected by blocked extract valves, duct restrictions or a fan fault.

4. The unit is louder than normal

A ventilation unit should produce a consistent operating sound. New or unusually loud noises may indicate that something has changed.

Listen for:

• Rattling
• Buzzing
• Grinding
• Whistling
• Increased fan noise

A clogged filter can increase resistance and cause some systems to work harder. Rattling may come from a loose cover or nearby component, while grinding or persistent buzzing may require professional investigation.

Always isolate the electrical supply before opening a unit and follow the manufacturer’s instructions. Electrical repairs should be completed by a suitably qualified person.

5. The filters are visibly dirty

Filters are particularly important in MVHR and PIV systems because they help prevent dust and debris from entering the unit or being supplied into the home.

The required inspection and replacement interval varies according to the unit, manufacturer and surrounding environment. Properties near busy roads, construction work or high levels of airborne dust may require more frequent checks.

Use the correct filter type and size for your unit. Browse BPC Ventilation’s range of replacement MVHR and PIV filters, or check the product manual before ordering.

Some controllers display a filter warning after a set period. Resetting the warning without inspecting or replacing the filter will not correct restricted airflow.

6. Boost mode or controls are not responding

MVHR and MEV systems may use wall switches, timers, humidity sensors or controllers to increase airflow when additional extraction is required.

Potential warning signs include:

• The unit remaining at one speed
• Boost mode failing to activate
• The system not returning to its normal setting
• A humidity sensor no longer responding
• An unresponsive controller or wall switch

Check the user controls and manufacturer’s troubleshooting guidance first. If the system remains unresponsive, a control, wiring or internal component may need to be tested.

7. The system displays an error message

Some ventilation units use warning lights, symbols or error codes to identify a possible fault.

The meaning of each code is specific to the manufacturer and model, so consult the correct product manual rather than assuming which component has failed. Repeatedly resetting the unit may temporarily remove a warning without resolving its cause.

Professional assistance may be required when an error relates to a fan motor, sensor, controller, electrical component or heat exchanger protection function.

How does maintenance differ between MVHR, MEV and PIV?

Although all three systems require clear airflow paths and working controls, their main maintenance areas are different.

You can explore BPC Ventilation’s ranges of MEV units and PIV units to see how the available systems and controls differ.

What ventilation maintenance can homeowners complete?

Depending on the system and manufacturer’s instructions, straightforward checks may include:

• Inspecting or replacing accessible filters
• Gently cleaning room valves and diffusers
• Checking that external grilles are not obstructed
• Looking for visible damage or loose connections
• Confirming that normal and boost settings respond correctly
• Checking the controller for warnings

Do not alter commissioned valve positions, dismantle fan motors or attempt electrical repairs unless you are qualified to do so.

For further technical information, the Passivhaus Trust MVHR Maintenance Guide provides detailed guidance on maintenance planning, service intervals and good practice.

For a more detailed MVHR checklist, read our existing guide to MVHR system maintenance.

Frequently Asked Questions

How often should a ventilation system be maintained?

There is no single interval suitable for every ventilation system. Follow the manufacturer’s maintenance schedule and check filters, valves and controls regularly. The required frequency can vary according to the model, property location and operating environment.

Can dirty filters cause condensation?

Dirty filters can restrict airflow in an MVHR or PIV system and may reduce its ability to manage indoor moisture effectively. However, condensation can also be caused by heating, insulation, moisture production and other property-related factors.

Should I turn my ventilation system off if it becomes noisy?

MVHR, MEV and PIV systems are generally designed to provide ongoing ventilation. Do not switch a system off permanently as a substitute for investigating the problem. Follow the manufacturer’s safety instructions and arrange professional assistance if the noise suggests a mechanical or electrical fault.

Keep Your Ventilation System Working Effectively

Regular checks can help identify airflow restrictions, dirty filters and control problems before they develop into more significant faults.

BPC Ventilation supplies replacement filters, ventilation units, controls and compatible system components from leading manufacturers. Contact our technical team when you need help identifying a suitable replacement product for your system.