We service air handling units across some of the UK’s most demanding environments — from busy office complexes to 24-hour manufacturing facilities. The one thing every site has in common is this: the units that get regular, structured maintenance run better, last longer, and cost far less to operate than the ones left to deteriorate.
This isn’t just theory. When we assessed four ageing AHUs at a commercial property in Dalston Cross, the primary issues — degraded bearings, failed damper actuators, and poor heat recovery performance — were all problems that a structured maintenance programme would have caught months earlier.
Effective AHU maintenance combines routine tasks performed frequently with periodic interventions addressing components on longer cycles. Here’s what we recommend based on decades of hands-on experience across commercial and industrial sites.
Why AHU Maintenance Matters
Neglected air handling units deteriorate progressively, with declining performance often going unnoticed until problems become acute. Energy consumption rises as components operate less efficiently. Air quality suffers as filtration effectiveness reduces. Comfort complaints increase as temperature control becomes erratic.
Beyond performance concerns, maintenance neglect risks unexpected failures that halt building ventilation entirely. We’ve attended emergency callouts where failed bearings, seized dampers, or motor burnouts have shut down entire buildings — creating costly disruption that proper maintenance would have prevented.
The cost of systematic AHU maintenance remains far below the cost of premature replacement or emergency repairs. We see it time and again on our maintenance contracts — the investment pays for itself many times over.
Daily and Weekly Checks
Visual Inspection
Brief daily visual checks identify developing problems before they cause failures. Walk-by inspection should note unusual noises, visible vibration, or warning lights indicating faults.
Fan operation sounds provide useful diagnostic information — our engineers can often diagnose problems just by listening. Changes in noise character typically indicate bearing wear, imbalance, or belt problems that need investigation.
Weekly inspection should include external panel condition, access door sealing, and any visible leaks or condensation indicating internal problems.
Operational Verification
Confirm AHU operation matches expected patterns. Systems not running when expected, or operating outside scheduled hours, indicate control problems requiring investigation.
Check that supply air temperatures match set-points. Deviation may indicate control faults, coil problems, or other issues affecting performance.
Filter Condition
Weekly filter checks remain essential despite any installed differential pressure monitoring. Visual inspection reveals filter conditions that sensors may not capture, including bypass, damage, or incorrect installation.
Record differential pressure readings to track filter loading trends. Accelerating pressure rise may indicate upstream problems introducing excessive contamination. We’ve seen cases where a sudden change in filter loading pointed to construction work elsewhere in the building drawing dust through the ventilation system.
Monthly Maintenance Tasks
Belt Inspection and Adjustment
Belt-driven fans require monthly inspection of belt condition and tension. Belts stretch over time, reducing drive efficiency and risking sudden failure.
Check belt alignment and adjust as necessary. Misalignment accelerates wear while wasting energy through friction losses. Tension should match manufacturer specifications — overtightening damages bearings while undertightening causes slippage.
Replace belts showing cracks, glazing, or excessive wear. Belt failure typically occurs without warning, halting AHU operation until replacement completes.
Damper Operation Check
Verify damper operation through full travel range. Dampers should move smoothly without binding or hesitation. Actuators should respond promptly to control signals.
Check damper blade sealing. Air leakage past closed dampers wastes energy and may compromise system control. When we carried out the assessment at Dalston Cross, failed damper actuators were one of the primary issues — the dampers had seized partially open, meaning the system was drawing in unconditioned outside air continuously and wasting significant energy.
Fire dampers require specific inspection procedures and should be checked according to their individual requirements and schedules.
Drain Pan Inspection
Condensate drain pans collect moisture from cooling coils. Blocked drains cause water accumulation risking overflow, water damage, and microbial growth.
Monthly inspection should confirm clear drains and proper pan drainage. Clean pans and drain lines as necessary to maintain drainage function.
Electrical Connections
Vibration and thermal cycling can loosen electrical connections over time. Monthly inspection of visible connections identifies potential problems before they cause failures.
Thermal imaging during operation identifies hot spots indicating high-resistance connections requiring attention. This non-invasive technique quickly assesses connection integrity across multiple points.
Quarterly Maintenance
Coil Cleaning
Heat exchanger coils accumulate contamination that reduces heat transfer efficiency. Quarterly cleaning maintains performance while preventing contamination buildup that becomes progressively harder to remove.
Cleaning method depends on coil type and contamination nature. Compressed air removes dry particulates. Coil cleaning solutions address greasy or biological contamination. High-pressure water suits heavily fouled coils.
Protect motors, controls, and other components from cleaning fluids. Ensure coils dry completely before returning units to service.
Fan Cleaning
Fan blades accumulate contamination affecting balance and efficiency. Quarterly cleaning maintains fan performance while preventing imbalance from uneven buildup.
Clean fan housings and scrolls. Accumulation in these areas restricts airflow while providing surfaces for further contamination buildup.
Motor Inspection
Inspect motor condition including temperature during operation, bearing noise, and any signs of overheating. Motors approaching failure often exhibit warning signs before sudden failure occurs.
Check motor cooling provisions. Blocked cooling air paths cause elevated temperatures accelerating insulation degradation. On our energy efficiency upgrade at Colmore Row, replacing aged motors with modern high-efficiency alternatives was one of the most impactful changes we made — the energy savings were immediate and substantial.
Control Calibration Check
Verify sensor accuracy against reference instruments. Drifting sensors cause control errors with energy and comfort implications.
Check actuator operation and calibration. Actuators should position accurately in response to control signals across their full range.
Six-Monthly Maintenance
Bearing Lubrication
Fan and motor bearings require lubrication at manufacturer-specified intervals, typically every six months for continuously operating equipment.
Use lubricants specified by equipment manufacturers. Incorrect lubricant selection can damage bearings. Apply correct quantities—over-lubrication causes problems as serious as under-lubrication.
Comprehensive Coil Inspection
Beyond quarterly cleaning, semi-annual inspection should assess coil condition more thoroughly. Look for corrosion, fin damage, and any signs of refrigerant or water leaks.
Check coil connections and headers. Thermal expansion and vibration stress connections that may develop leaks over time.
Ductwork Connection Inspection
Inspect flexible connections between AHU and ductwork. These connections absorb vibration but deteriorate over time. Damaged flexible connections allow air leakage and noise transmission.
Check ductwork sealing at AHU discharge. Poorly sealed connections waste energy while potentially creating comfort problems from uncontrolled airflow.
Safety Device Testing
Test safety interlocks and protective devices. High-pressure switches, temperature limits, and other safety devices must operate correctly to protect equipment and occupants.
Document test results and address any devices failing to operate within specifications.
Annual Maintenance
Comprehensive Performance Assessment
Annual assessment should establish complete performance baseline. Measure air flow rates, pressure differentials, and energy consumption under representative operating conditions.
Compare current performance against design specifications and previous annual assessments. Declining trends indicate developing problems requiring intervention. This kind of annual assessment is exactly what led to the scope of work at Dalston Cross — without a structured review, the deterioration across all four units would have continued unchecked.
Structural Inspection
Inspect AHU casing and framework for corrosion, damage, and deterioration. Address problems before they progress to affect unit integrity or performance.
Check insulation condition inside casings. Damaged insulation reduces thermal performance while potentially introducing contamination.
Motor Testing
Annual motor testing should include insulation resistance measurement and vibration analysis. These tests identify developing problems before sudden failure occurs.
Consider motor efficiency assessment, particularly for older installations. Modern high-efficiency motors may justify replacement based on energy savings alone.
Heat Recovery System Service
Heat recovery systems require specific maintenance beyond general AHU tasks. Plate exchangers need inspection for damage and accumulated contamination. Thermal wheels require drive system attention and media inspection.
Check bypass dampers operate correctly for frost protection and summer operation. Verify defrost systems function as designed.
Control System Review
Annual control system review should assess programming against operational requirements. Requirements may have changed since original commissioning.
Update control strategies to exploit any efficiency opportunities identified through operational experience.
Creating a Maintenance Schedule
Effective maintenance requires systematic scheduling. CMMS systems track task scheduling, completion recording, and history retention — but even a simple spreadsheet provides structure. The discipline of scheduled maintenance delivers benefits regardless of tracking sophistication.
Task Prioritisation
Safety-related tasks take priority over efficiency-focused activities. When resources are constrained, prioritisation ensures critical tasks complete even if lower-priority items defer.
Seasonal Considerations
Schedule heating coil maintenance in summer when heating demand is minimal. Cooling system attention fits winter schedules. Major activities suit building low-occupancy periods.
Documentation
Consistent documentation enables trend identification across maintenance cycles, revealing developing problems through pattern recognition.
Working with Maintenance Contractors
Many organisations engage specialist contractors for AHU maintenance. We work with facilities teams across the UK on both planned maintenance contracts and one-off assessments.
The key to effective contractor relationships is clear specifications. Maintenance contracts should specify required tasks, frequencies, and standards — vague specifications lead to disputes about scope and quality. Include performance expectations where appropriate. Contractors should maintain specified conditions, not simply complete listed tasks.
How We Can Help
i-Flow Technologies supports facilities teams with AHU maintenance, from routine planned programmes to complex refurbishment projects. Our engineers bring decades of hands-on experience across commercial, industrial, and specialist applications.
Whether you need a one-off assessment, ongoing maintenance contract, or advice on an ageing system, we’re here to help. Contact us to discuss your AHU maintenance requirements.
