The Maintenance Guide: A Lifecycle Checklist for Ventilation Systems

Under Approved Document Part F 2021, dwelling ventilation systems must be maintained to continue meeting minimum ventilation requirements. For rental properties, this creates a clear landlord obligation that aligns with the Awaab's Law compliance framework: a system that is not maintained is a system that may not be providing adequate ventilation, which is both a regulatory and a health risk.

For owner-occupiers, the case is equally straightforward. An MVHR unit operating with a partially blocked supply filter consumes more fan energy to deliver the same airflow, recovering less heat per unit of electricity consumed. The energy efficiency benefit you invested in is being eroded by a component change that takes five minutes.

Every 3 Months: Occupant-Level DIY Tasks

Visual inspection of all terminal grilles and valves

Grilles should be free of dust accumulation, undamaged, and unobstructed by furniture, curtains, or stored items. Obstructed supply valves create pressure imbalance, increasing fan speed and noise, and reducing airflow to the affected room. Clean with a soft brush or vacuum attachment.

Check and replace supply and extract filters (if indicator signals)

Most modern MVHR units incorporate differential pressure sensors that illuminate a filter-change indicator when pressure drop across the filter exceeds the design threshold. This is the primary indicator to act on. For units without indicators, filter condition should be physically inspected every three months. In high-dust or high-pollen environments, quarterly filter replacement is appropriate regardless of indicator status.

Filter classes for residential MVHR: G4 coarse filters protect the heat exchanger and fans; F7 or higher fine filters on the supply side provide allergen and PM2.5 filtration. Both classes must be replaced, not cleaned.

Check condensate drain (if applicable)

MVHR units operating in winter climates generate condensate from moisture removed from the extracted air stream. The condensate trap and drain line must be clear. A blocked drain causes water to accumulate in the unit, potentially damaging the heat exchanger core and causing mould growth within the casing.

Every 6 Months: Householder-Level Tasks

Clean heat exchanger core

The counter-flow heat exchanger core accumulates fine particulate over time. On most residential units, the core is accessible without tools—refer to the manufacturer's installation and maintenance manual. Remove and wash gently with lukewarm water; do not use detergent. Allow to dry fully before reinstallation. A fouled core reduces heat recovery efficiency by 10–20%.

Inspect duct connections at unit

Flexible anti-vibration connections at the MVHR unit inlet and outlet can work loose over time. Check that all connections are airtight and properly supported. Loose connections allow recirculation of extract air into supply—a cross-contamination risk and a source of poor IAQ.

Check external terminals for blockage

External supply and exhaust terminals are susceptible to bird nesting, insect ingress, and debris accumulation. Inspect from ground level; remove any blockages. Check that terminal cowls are undamaged and correctly oriented (typically pointing downwards to prevent rain ingress).

Annually: Professional Service Visit

Full recommissioning of airflow rates

A professional engineer measures actual airflow at every supply and extract terminal and compares measured rates against the commissioned design values. Where rates have drifted—due to filter loading, duct movement, or balance damper displacement—dampers are readjusted to restore the designed distribution.

This is not an optional task. Airflow rates that have fallen below Part F minimum values represent a compliance failure. A professional annual service restores compliance and provides a documented record—essential for landlord compliance and building warranty purposes.

Fan inspection and bearing check

EC motor fans are largely maintenance-free, but annual inspection confirms correct rotation, checks for vibration (indicating bearing wear), and cleans any accumulated dust from the impeller. An unbalanced impeller generates noise and accelerates bearing failure.

Controls and sensor calibration check

Humidity sensors should be verified against a calibrated reference. CO2 sensor manufacturers typically recommend a single-point calibration check every 12–24 months; Flexivent carries calibration equipment and performs this check as part of the annual service.

Ductwork inspection (visual, accessible sections)

Accessible ductwork sections are inspected for damage, condensation staining (indicating an insulation deficiency), and joint integrity. Any defects identified are documented and remediated before sign-off.

Every 3–5 Years: Major Maintenance Intervals

Full duct inspection including inaccessible sections

Where ductwork passes through voids and cannot be visually inspected, a flexible camera inspection confirms duct integrity, identifies any internal condensation accumulation, and checks for bird or rodent ingress at external terminals.

Heat exchanger replacement assessment

Counter-flow heat exchanger cores have a typical service life of 10–15 years with good maintenance. At the five-year service interval, Flexivent engineers assess core condition and project remaining service life. Where efficiency has measurably declined through fouling that cannot be reversed by cleaning, core replacement is recommended before the system reaches the end of its economic operating life.

Full system recommissioning to current standards

At five-year intervals, a comprehensive recommissioning exercise verifies that the installed system continues to meet current Part F minimum ventilation rates for the as-occupied dwelling. Where property use has changed—additional bedrooms, wet rooms, or open-plan reconfiguration—the design ventilation rates are recalculated and the system adjusted accordingly.

Positive Input Ventilation units have a simpler maintenance profile: inspect the loft-mounted filter every six months and replace annually; check the unit's indicator light; verify that the inlet duct from the external terminal is unobstructed. Centralised MEV systems require annual inspection of the central fan unit, filter replacement, and grille cleaning.

Flexivent offers structured maintenance agreements for residential MVHR, PIV, and MEV systems across the UK. Our engineers carry manufacturer-approved filters, calibration equipment, and airflow measurement instrumentation to every service visit, and issue a signed compliance certificate confirming the system's continued performance against Part F requirements.

Contact Flexivent today to arrange your annual service or to enquire about our ongoing maintenance plan. A properly maintained ventilation system protects your health, your compliance, and the value of your property for the life of the building.