An MVHR system works quietly throughout the year, bringing fresh air into living rooms and bedrooms while removing humid, stale air from kitchens and bathrooms. Because it runs in every season, its maintenance needs change with the weather.
A useful MVHR maintenance checklist is not a long list of technical jobs. It is a small set of timely checks that protect airflow, filtration and the heat exchanger. Most are safe for a homeowner; faults involving wiring, fans, ductwork or system balancing belong with a qualified engineer.
Why seasonal MVHR maintenance matters
Filters collect different loads during the year, from spring pollen to winter dust. Outside terminals face leaves, insects, frost and wind-driven debris, while the condensate drain is busiest in colder weather. Checking the right component at the right time makes problems easier to spot before comfort suffers.
Spring: clear winter build-up
Replace filters before pollen season
Open the unit only as the manual directs, isolate it if instructed and inspect both filters. A darkened surface, a replacement alert or weaker airflow may mean they are due. Use the specified dimensions and filter grade; owners of compatible units can find replacement systemair filters by model. Do not wash a disposable filter unless its instructions expressly allow it.
Check the outside terminals
From a safe position, look for leaves, cobwebs, nesting material or other debris around the intake and exhaust. Clear only what is readily accessible and avoid pushing dirt into the duct. High-level terminals and damaged grilles should be left to a professional.
Summer: manage pollen and heat
Watch how quickly filters load
Homes near busy roads, building work, fields or mature trees may load filters faster in summer. A quick mid-season inspection is more useful than relying on one fixed calendar date. Follow the unit’s warning display and the manufacturer’s replacement schedule.
Understand summer bypass
Many MVHR units can bypass the heat exchanger when outdoor air is cooler than indoor air. This may help with night-time cooling, but it is not air conditioning and cannot overcome strong solar gain. Keep blinds closed before rooms overheat and use the bypass settings described in the manual.
Autumn: prepare for heating season
Clean valves without changing their position
Dust around supply and extract valves can be wiped away gently. Do not twist the centre disc or swap valves between rooms: their positions may have been set during commissioning to balance airflow. Grease-heavy kitchen terminals may need more careful cleaning.
Check condensate drainage
As heat recovery increases in cooler weather, condensation forms inside the unit and should drain away. Look for visible leaks, an overflowing tray or an unusual gurgle. A blocked, dry or incorrectly fitted trap can cause trouble, so consult the manual or arrange a service rather than dismantling the drain.
Winter: look for moisture, frost and noise
Temporary changes in fan speed can be normal when frost protection operates in very cold weather. Persistent weak airflow, water around the unit, new vibration or repeated alarms are not. Check that accessible external terminals are clear of snow or ice, but never climb onto a roof in poor conditions.
Keep the system running
MVHR is designed to ventilate continuously. Turning it off for long periods can allow humidity, odours and indoor pollutants to build up, particularly when windows remain closed. Use normal or boost modes as intended rather than switching the unit off to silence an unexplained noise.
A short check every month
Notice how the home feels. Lingering bathroom condensation, stuffy bedrooms, whistling valves, a sudden rise in fan noise or a warning symbol all deserve attention. Confirm the operating mode, inspect filters when safe and keep the area around the unit unobstructed.
Know when to call an engineer
Arrange professional help for electrical faults, leaks, damaged ductwork, persistent alarms or airflow that remains uneven after basic checks. The system may need measured airflow testing and rebalancing rather than a higher fan setting.
Seasonal MVHR maintenance is most effective when it becomes routine. A few well-timed checks help the system deliver cleaner air reliably, while early professional attention prevents a small warning sign from becoming an inconvenient failure. A dated note of each inspection also makes emerging patterns easier to recognise.
