Generator set faults: the most common issues and how to prevent them

In hospitals, data centres, industrial facilities, transport infrastructure or telecommunications installations, their availability can be critical.

However, like any electromechanical equipment, a generator set consists of various systems that require monitoring and maintenance. A deteriorated battery, contaminated fuel, a cooling system problem or a seemingly minor alarm can prevent the unit from responding correctly when required.

Understanding the most common faults in generator sets, identifying their symptoms and taking preventive action is essential to minimise the risk of downtime and ensure system availability.

Not all incidents have the same origin or severity. Some are related to the engine itself, while others affect auxiliary systems such as the batteries, fuel circuit, cooling system, alternator or control system.

Furthermore, an alarm does not necessarily mean that there is a serious fault. Modern control and monitoring systems are specifically designed to detect deviations before they can lead to more significant damage.

In critical installations, the objective should be precisely the opposite: to detect and correct anomalies before they affect equipment availability.

The most common faults in generator sets include starting problems, fuel supply issues, overheating, lubrication faults and certain electrical or control-related incidents.

When a generator set fails to start, one of the first elements that should be checked is the battery system.

The batteries remain ready to supply the energy required during the starting process and, in standby units, they may remain for long periods without the generator actually being called into service. Ageing, insufficient charge or poor connections can progressively reduce their capacity.

The most common problems include:

• Discharged or deteriorated batteries.
• Battery charger failures.
• Dirty, loose or corroded terminals.
• Faulty electrical connections.
• Loss of capacity due to ageing.

In a critical installation, checking voltage alone is not enough. Periodically assessing the actual condition of the batteries makes it possible to anticipate one of the failures that can most directly compromise the unit’s ability to start.

Fuel is another element that requires particular attention, especially in standby generator sets that may remain unused for long periods.

The presence of water, sediment or contaminants in the fuel can cause blockages, injection problems, starting difficulties or irregular engine operation.

Other issues may include:

• Blocked fuel filters.
• Air entering the circuit.
• Insufficient fuel level.
• Pump or fuel transfer system failures.
• Leaks in pipes or connections.
• Fuel stored for long periods under unsuitable conditions.

For this reason, maintenance should not be limited to the engine itself. The tank, filters, pipework and auxiliary fuel supply systems form part of the same overall system and should be inspected in a coordinated manner.

The engine generates a considerable amount of heat during operation and needs to maintain its temperature within specified parameters.

When the cooling system is unable to dissipate this heat correctly, the temperature rises and the generator set’s protection systems may shut the unit down to prevent damage.

Possible causes include:

• Insufficient coolant level.
• Leaks in the circuit.
• Dirty or blocked radiators.
• Fan problems.
• Cooling pump or thermostat failures.
• Deteriorated belts or hoses.
• Insufficient airflow within the installation.
• Ambient temperatures above those considered during the design stage.

Ventilation within the generator room also plays a fundamental role. It is not enough for the generator set itself to be properly maintained: the installation must provide adequate air intake and heat dissipation.

This is particularly important in technical rooms, industrial facilities or equipment located in spaces where environmental conditions can vary significantly.

The lubrication system protects the internal engine components against friction and helps ensure correct operating conditions.

An insufficient oil level, a leak or lubrication pressure outside the specified range can trigger alarms and may even cause the unit to shut down automatically.

Possible causes include:

• Incorrect oil level.
• Degraded oil.
• Blocked filters.
• Leaks.
• Faulty sensors.
• Problems within the lubrication circuit.

Using the oil specified by the manufacturer and following the corresponding maintenance intervals is essential to reduce engine wear and extend its service life.

A generator set may start correctly and yet fail to generate the expected voltage or may produce electrical values outside the specified parameters.

In these cases, the fault may be located in different parts of the electrical system:

• Alternator.
• Deterioration of winding insulation due to moisture or ageing, detectable by insulation resistance measurements.
• Automatic Voltage Regulator (AVR) and excitation system.
• Protection circuit breakers.
• Wiring.
• Connections.
• Measuring or protection devices.

Symptoms may range from a complete absence of voltage to fluctuations, incorrect values or the activation of specific protection systems.

Fault diagnosis of this type should be carried out by qualified personnel, as working on power generation systems involves risks and requires specialist knowledge and equipment.

Modern generator sets incorporate electronic systems that monitor numerous variables, including temperature, pressure, engine speed, fluid levels, voltage, frequency, battery condition and a wide range of external signals.

An alarm can prevent the unit from starting or stop it when the controller detects a condition that it considers unsafe.

Common issues may be related to:

• Sensors.
• Signal wiring.
• Controller configuration.
• Communications.
• Activated emergency stops.
• The unit being set to manual mode when it should be in automatic mode.
• Alarms that have not been correctly acknowledged or reset following an intervention.

For this reason, whenever an incident occurs, it is essential to review the alarm history and analyse the actual condition that caused the fault rather than simply clearing the warning.

Remote monitoring greatly facilitates this process, as it enables parameters, trends and alarms to be supervised and certain deviations to be detected before they lead to a system shutdown.

In emergency installations, power availability does not depend solely on the generator set.

When the mains supply fails, the system must detect the outage, initiate generator start-up and transfer the load using the corresponding changeover system.

It is therefore possible for the generator set itself to operate correctly while a problem prevents the transfer of power to the installation.

Periodic inspections should verify the operation of the complete system:

mains supply → fault detection → start-up → stabilisation → load transfer → power supply to the installation → mains restoration → retransfer to mains → generator cool-down and shutdown.

This integrated approach is particularly important in installations where even a few seconds of interruption can have significant operational consequences.

Leaks are among the symptoms most easily detected during a visual inspection and, precisely for this reason, they should never be ignored.

They may occur in:

• Hoses.
• Fittings.
• Seals and gaskets.
• Pumps.
• Radiators.
• Pipework.
• Tanks and auxiliary systems.

A minor leak can develop to the point where it causes sufficient loss of pressure or fluid level to affect equipment operation.

Regular inspections allow these anomalies to be identified before they develop into a more serious fault.

The engine needs to receive a sufficient quantity of clean air to ensure proper combustion.

Air filters can gradually accumulate dust and particles, particularly when the generator set is installed in industrial environments, areas with high concentrations of airborne particles or locations subject to demanding environmental conditions.

A poorly maintained air intake system can lead to reduced performance, inefficient combustion or increased fuel consumption.

Oil and fuel filters, covered in the previous sections, should also be inspected and replaced in accordance with the manufacturer’s maintenance instructions.

A generator set should be selected according to the actual power requirements and load profile of the installation.

An excessively oversized unit should not operate for prolonged periods at very low loads, as this can encourage incomplete combustion and the accumulation of deposits in certain diesel engines.

Over time, continuous operation outside suitable operating conditions can affect performance and increase maintenance requirements.

For this reason, correct generator sizing affects not only the initial investment or fuel consumption. It also has an impact on how the engine operates and on the reliability of the installation throughout its service life.

A fault can rarely be attributed to a single cause that applies to every generator set.

The likelihood of failure depends on factors such as:

• Operating hours.
• Equipment age.
• Frequency and quality of maintenance.
• Environmental conditions.
• Type of application.
• Fuel quality.
• Load profile.
• Installation design.
• Frequency of testing.
• Condition of auxiliary systems.

A generator set used as a prime power source operates under completely different conditions from a standby unit that only starts when the mains supply fails.

Maintenance should therefore be defined specifically for each installation.

The best way to reduce the likelihood of a fault is to detect potential problems before they occur.

A preventive maintenance programme makes it possible to identify wear, leaks, parameter deviations or components approaching the end of their service life before they cause an unexpected shutdown.

Visual inspections make it possible to identify quickly:

• Leaks.
• Incorrect fluid levels.
• Deteriorated connections.
• Alarms.
• Corrosion.
• Dirt or build-up of debris.
• Visible damage.

A minor anomaly may be the first sign of a more serious problem.

System availability begins with ensuring that the engine is able to start.

Checking the batteries, chargers and connections should form part of every preventive maintenance programme.

Fluids are essential to engine operation. Both their levels and their condition must be checked, while circuits should be kept free from leaks and contamination.

A standby generator set may remain unused for weeks or months.

It must therefore be tested periodically.

In addition to verifying start-up, testing under load makes it possible to assess the system’s actual behaviour and detect problems that may not be apparent during a simple no-load test.

Temperatures, pressures, voltages, frequencies, fluid levels and battery status provide valuable information about the condition and development of the equipment.

Monitoring and trend analysis make it possible to move from purely reactive maintenance towards preventive and predictive strategies.

The first step is to correctly identify the origin of the problem.

When an alarm or unexpected shutdown occurs, it is advisable to record:

• Alarm code and description.
• Time at which the event occurred.
• Load conditions.
• Parameters recorded prior to shutdown.
• Behaviour observed during start-up or operation.
• Any recent interventions.

This information can significantly facilitate subsequent diagnosis.

Electrical, mechanical or fuel-system interventions should be carried out by qualified personnel. An incorrect intervention may worsen the fault, compromise protection systems or create risks for both people and the installation.

Waiting for a generator set to fail before intervening means adopting a purely corrective maintenance strategy.

In critical installations, the objective should be precisely the opposite: to detect and correct anomalies before they affect equipment availability.

Preventive maintenance, periodic testing, monitoring and component condition analysis help to:

• Reduce unexpected shutdowns.
• Anticipate component replacement.
• Extend equipment service life.
• Improve operational safety.
• Optimise maintenance costs.
• Increase installation availability.

In applications where power continuity is essential, having a maintenance plan adapted to each generator set and its actual operating conditions is just as important as selecting the correct generator set in the first place.

At Genesal Energy, we consider after-sales service an essential part of the reliability of any power solution.

Our After-Sales Service provides preventive and corrective maintenance for generator sets, commissioning, monitoring and specialist support for installations where power availability is a priority.

A generator set consists of various systems that require monitoring and maintenance.

We have specialist professionals, a technical support network and a 24/7 service to respond to incidents and help ensure that equipment remains ready to operate whenever it is needed.

Because in a critical installation, resolving a fault is important. Anticipating it is even more important.

Why does a generator set fail to start?

There can be many different causes. The most common include a discharged or deteriorated battery, a starter motor or preheating system fault, fuel system problems, an active alarm, an activated emergency stop or an anomaly detected by the control system. A proper diagnosis is required to identify the specific cause.

How can generator set faults be prevented?

The main measure is to implement a preventive maintenance programme adapted to the equipment and its operating conditions. Checking batteries, fluids, filters, electrical and control systems and carrying out regular tests helps detect many problems before they cause a shutdown.

How often should a generator set be serviced?

There is no single interval that applies to all equipment. The frequency depends on the model, operating hours, type of application and environmental conditions. The manufacturer’s specifications should be followed and a maintenance plan appropriate to each installation should be established.

Does a generator set need to be tested even if it is not used?

Yes. Standby generator sets should undergo periodic checks even if they have not been required to supply power. Testing makes it possible to verify start-up, check the condition of auxiliary systems and detect anomalies before an actual emergency occurs.