Troubleshooting Common Issues in Commercial Heat Recovery Systems

Even the most robust heat recovery system will eventually run into problems. On a complex commercial site, it's not a question of if, but when. A sudden drop in performance, a strange new noise, or a fault code flashing on a controller can quickly turn a building's biggest energy-saving asset into a liability. The key isn't just fixing the problem; it's diagnosing it quickly and accurately to minimise downtime and wasted energy.

Effective HRV troubleshooting is a process of elimination, starting with the simple and obvious before moving to the complex. It requires a systematic approach, not guesswork. Too many engineers jump straight to the most complicated conclusion, overlooking a simple blockage or a tripped switch. Understanding the common failure points is the first step toward becoming efficient at solving these inevitable HVAC system issues.

The First Rule: Observe Before You Act

Before a single tool comes out of the bag, the first job is to observe the system and gather information. What are the actual symptoms? It's easy for a facilities manager to just say "it's not working," but the details matter. Is the air not warm enough? Is there no airflow from the grilles? Is the unit making a rattling sound? Is there water pooling underneath it?

This initial diagnosis is like a doctor asking a patient about their symptoms. You can't find the cure until you understand the illness. Check the controller for any active alarms or fault codes. This information, combined with your own observations, will point you in the right direction and stop you from chasing phantom problems.

Common Culprit #1: Airflow Faults

The vast majority of performance issues in a heat recovery system are related to airflow. If the right amount of air isn't moving through the unit, it simply cannot work correctly.

The Filter Blockage

This is, without a doubt, the most common fault. Clogged filters are the enemy of efficiency. As dust and debris build up, the resistance to airflow increases, forcing the fans to work harder and harder just to maintain volume. Eventually, they can't keep up. The result is reduced ventilation, poor heat transfer, and a massive spike in energy consumption. Filters should be the very first thing you check in any HRV troubleshooting scenario.

Fan and Motor Problems

If the filters are clean but airflow is still low, the fans are the next logical suspect. In older units with belt-driven fans, a loose or snapped belt is a common point of failure. In modern direct-drive fans, the issue is more likely to be electrical. Listen for unusual noises like grinding or humming, which could indicate failing motor bearings. A thermal camera can be a useful tool here, showing if a motor is running excessively hot.

Ductwork Issues

The problem isn't always inside the unit itself. The ductwork that connects the unit to the building is a frequent source of trouble. Flexible ducts can easily get crushed or kinked during unrelated work in a ceiling void, restricting airflow. Joints can become disconnected, leading to huge air leaks where conditioned air is lost before it ever reaches the room.

An Engineer's Tale: The Phantom Fault

A call came in for a newly installed system in a large retail unit. The staff were complaining of drafts, and the unit was flagging an intermittent fan fault. The installation company had been back three times, replacing sensors and even swapping the fan motor, but the problem persisted. The client was losing faith fast.

On arrival, the unit itself seemed fine. But a quick check in the ceiling void revealed the issue. A section of the main supply duct, a large-diameter flexible hose, had sagged and formed a U-bend, which had filled with condensed water. The weight of the water was almost completely sealing the duct. The fan was trying to push against this blockage, causing it to overcurrent and trip its internal protection, which logged the fault. Draining the water and properly supporting the ductwork fixed the problem permanently. It was a classic example of one of the most overlooked HVAC system issues: assuming the problem is with the main unit, not the infrastructure connected to it.

Common Culprit #2: The Heat Exchange Process

If airflow is good but the system isn't recovering heat effectively, the problem lies with the heat exchanger core or its associated components.

The Dirty Heat Exchanger

Over time, a fine layer of dust can get past the filters and coat the delicate surfaces of the heat exchanger. This film acts like a layer of insulation, preventing heat from transferring efficiently between the two air streams. The solution is to remove the core and clean it carefully according to the manufacturer's guidelines.

Condensate Drain Blockage

This is a critical and potentially damaging fault. As warm, moist air is cooled, water condenses and is collected in a tray. A small drain pipe is supposed to carry this water away. This drain is the perfect environment for sludge and mould to grow, which can quickly cause a blockage. A blocked drain is like a blocked sink; the water has to go somewhere. It will back up, overflow the tray, and spill into the unit's interior, corroding electrical components and potentially causing thousands of pounds worth of damage. Checking and clearing the condensate trap should be a mandatory part of every service.

Common Culprit #3: Control and Sensor Failures

Modern systems are heavily reliant on sensors and controllers to operate. When these fail, the system can behave in very strange ways.

Inaccurate Sensor Readings

A temperature sensor that is reading 5°C higher than the actual temperature can trick the system into thinking it doesn't need to recover as much heat. A faulty CO2 sensor can keep the system running at full speed even in an empty building. Verifying sensor readings against a calibrated handheld meter is a vital step in any deep diagnostic.

Actuator and Damper Failure

Motorised dampers control the flow of air for functions like frost protection or summer bypass. If the actuator motor fails, these dampers can get stuck in the wrong position, severely compromising performance. You might find a system trying to heat a building in winter with the summer bypass damper stuck wide open.

Sourcing Reliable Replacement Parts

When troubleshooting reveals a failed component, the quality of the replacement part is crucial. Using a cheap, non-approved part is a false economy that can lead to repeated failures and even damage other parts of the system. It's essential to use genuine, high-quality components from trusted manufacturers.

This is where a supplier with real technical expertise proves its worth. The team at National Pumps and Boilers has the in-depth knowledge to identify the correct part for any commercial system, stocking components from leading brands like ATAG and Lowara. They ensure you get a replacement that restores the system to its original specification. For expert help in sourcing the right parts for a repair, it’s always best to get in touch with specialists.