A UK Engineer’s Guide: 7 Common Air Compressor Problems and How to Fix Them

Compressed air is an essential utility for the UK industry. A system failure can halt production and increase operational costs. Understanding common air compressor problems is the first step to maintaining uptime.

This guide details seven common air compressor problems and their solutions. It covers safe, in-house checks and explains when to call a professional service engineer for support.

A Non-Negotiable First Step: Safety and UK Regulations

Safety is the absolute priority before any diagnostic work. An air compressor stores significant electrical and pneumatic energy. As certified engineers at Control Gear, we consider established safety protocols a mandatory part of any maintenance task.

Isolating Energy: The Lockout/Tagout (LOTO) Procedure

The machine must be in a zero-energy state before any work begins. A full LOTO procedure includes these steps:

1. Preparation & Notification: Identify all energy sources. Notify affected personnel of the shutdown.
2. Shutdown: Use the compressor’s normal shutdown sequence.
3. Isolation: Turn the main electrical isolator to “OFF” and apply a padlock.
4. Tagout: Attach a durable tag to the padlock, stating “Do Not Operate” and identifying the engineer.
5. Dissipate Stored Energy: Open a manual drain valve to release all air pressure. The system gauge must read zero. Ensure stored electrical energy in components has been safely discharged.
6. Verification: Attempt to start the compressor. It should be completely unresponsive.

Your Legal Duty: Pressure Systems Safety Regulations 2000 (PSSR)

If the combined metric of your system’s pressure vessel size (capacity in litres) multiplied by its working pressure is greater than 250 bar-litres, then your system will fall under PSSR. PSSR requires the preparation of a Written Scheme of Examination (WSE) by a “Competent Person” and then a cycle of statutory inspections in accordance with the WSE. Failure to comply can result in very large fines. We can provide your WSE and statutory inspections so that you are 100% compliant.

Here are the seven most common issues we see in UK industrial facilities.

Problem 1: Compressor Fails to Start

Symptoms

The machine is unresponsive. The motor may hum but does not turn, or the circuit breaker trips upon starting.

Potential Causes

• Power Supply: A tripped facility breaker, engaged emergency stop, or main isolator in the “OFF” position is a common cause.
• Safety Interlocks: Low oil levels can trigger a safety switch that prevents startup.
• Component Failure: A humming motor often indicates a faulty start capacitor. A seized motor or air-end is a more serious issue.
• High Starting Load: A faulty unloader valve prevents trapped air from venting. The motor then attempts to start against high pressure, causing an overload.

Safe DIY Checks You Can Carry Out

• Perform the full LOTO procedure first.
• Check that the main electrical isolator is “ON”. Reset any tripped breakers at the facility panel.
• Ensure all emergency stop buttons are disengaged.
• Check the oil level. Fill it up with the lubrication recommended by the manufacturer if it’s low.

When Should You Call a Professional Engineer?

• The circuit breaker keeps tripping.
• The motor hums but does not turn. This likely requires capacitor replacement or investigation of a seizure.
• It is a visible struggle with the compressor against the pressure before tripping, which suggests a valve problem.
• The monitoring system (SMARTLINK by Atlas Copco) may send an alarm signal with information about a continuing fault that requires diagnostic work.

Problem 2: Insufficient Air Pressure

Symptoms

Air-powered tools underperform. The compressor struggles to reach the proper pressure, even after prolonged operation.

Potential Causes

• Air Leaks: Leaks are a primary cause of pressure loss and wasted energy. A system can lose up to 30% of its air production through leaks in fittings, couplers, and hoses.
• Clogged Filters: A blocked air filter reduces intake volume. A clogged inline filter restricts downstream flow.
• Demand Exceeds Capacity: New machinery might create an air demand that surpasses the compressor’s capacity.

Safe DIY Checks You Can Carry Out

• Perform a Leak Audit: On a slow day, turn off the compressor, pressurise the system, and listen out for hissing sounds. Dab a soapy water solution on joints; bubbles will reveal leaks.
• Inspect Intake Filter: After LOTO, inspect the air filter. If dirty, replace it to restore performance.

When You Should Contact a Professional Engineer

• Pressure remains low after fixing leaks and changing filters. This suggests an internal problem.
• You require a professional Compressed Air Leak Detection survey with ultrasonic equipment. For chronic leaks, upgrading to a leak-free piping system (e.g., AIRnet) is a permanent solution.

Problem 3: Compressor Overheating

Symptoms

The alarm system activates a high temperature warning/alarm or initiates a shutdown. The unit feels hotter to the touch than it typically would.

Potential Causes

• Subpar Ventilation: A compressor can blow its own hot discharge air across its cooler in a small or enclosed area. This then raises the temperature.
• Incorrect Oil Level: Oil is used as a coolant; a low oil level or wrong type of oil, decreases cooling capacity.
• Dirty Coolers: Oil cooler and aftercooler fins clogged with dust and debris insulate the heat transfer media from air-cooling.
• Internal Fault: A failed thermostatic bypass valve (in oil cooler line) will not allow oil to pass through the cooler.

Safe DIY Checks You Can Carry Out

• Improve Ventilation: Clear at least one metre of space around the compressor.
• Check Oil Level: Check oil level after LOTO and when the unit is cool, top up if necessary.
• Clean the Coolers: Isolate the machine. Remove dust from cooler fins with low pressure air.

When You Should Contact a Professional Engineer

• The compressor continues to overheat after these checks are complete.
• A faulty thermostatic valve is suspected. Modern systems, like the cooling units in VSD compressors, are highly efficient; an overheating often signals an underlying fault.

Problem 4: Excessive Oil in Air Lines

Symptoms

Oily residue is present in system condensate. An oily mist is expelled by pneumatic machinery, otherwise downstream filters rapidly become saturated.

Potential Causes

• Saturated Separator Element: Oil aerosols can pass through the oil separator filter if it gets blocked or damaged.
• Blocked Scavenge Line: This tube returns collected oil from the separator to the sump. If it clogs, the oil is carried downstream.
• Oil Overfill: An overfilled oil reservoir can overwhelm the separation system.

Safe DIY Checks You Can Carry Out

• Check the Oil Level: Verify that the oil level is below the maximum fill line following LOTO.
• Verify Lubricant: Ensure the correct type of specialised compressor oil is in use.
• Address Overheating: High temperatures increase carry-over and decrease oil viscosity. So, first, you must fix any overheating problems.

When You Should Contact a Professional Engineer

• The oil level, type, and temperature are correct. This indicates the fault is internal.
• A technician is needed to replace the oil separator or unclog a clogged scavenge line.
• An oil-free compressor is the best option for demanding applications. Make sure you have the appropriate Compressed Air Quality Filters for your existing systems.

Problem 5: Excessive Moisture in Air Lines

Symptoms

Liquid water is discharged from tools, causing malfunction or corrosion. Rust may be visible inside pipework.

Possible Explanations

• Faulty Draining: Drains can malfunction due to sludge buildup caused by automatic condensate.
• Failure of the Air Dryer: The dryer may be broken, turned off, or too small for the humidity and airflow.
• High Humidity: A drying system built for ordinary conditions may be strained by excessively humid weather.

Safe DIY Checks You Can Carry Out

• Manually Drain the Receiver: As a daily check, open the manual drain on the tank. A large discharge of water suggests the automatic drain is not working.
• Inspect Automatic Drains: Observe auto-drains during operation to ensure they discharge periodically.
• Check the Air Dryer: Confirm the unit has power and check for any fault lights on its control panel.

When You Should Contact a Professional Engineer

• Automatic drains are not functioning and need to be serviced or replaced.
• An air dryer has a fault, such as a refrigerant leak or saturated desiccant.
• Your operation requires a professional audit to specify the correct type and size of Air Compressor Dryers.

Problem 6: Unacceptable Noise or Vibration

Symptoms

New sounds, including rattling, grinding, or a high-pitched screech, are produced by the compressor. The unit may vibrate excessively.

Potential Causes

• Free Components: Safety guards, panels, and mounting bolts may come free as a result of vibrations over time.
• Drive Belt Problems: The drive belt may make slapping, whining, or screeching sounds if it is too tight, too loose, or worn out.
• Worn Bearings: This is a critical issue. A deep, rhythmic grinding sound is a classic sign of bearing failure.

Safe DIY Checks You Can Carry Out

• Perform the full LOTO procedure.
• Check and tighten all accessible mounting bolts, panels, and guards.
• Inspect drive belts for wear and correct tension.

When You Should Contact a Professional Engineer

• Immediately shut the machine down for any deep grinding or knocking noises. This is an urgent warning of bearing failure and can prevent a complete seizure.
• Any abnormal noises from the air-end of a rotary screw compressor require expert diagnosis.

Problem 7: Compressor Runs Continuously

Symptoms

The compressor motor runs non-stop and never reaches its cut-off pressure. The safety relief valve may open.

Potential Causes

• High Demand or Major Leak: Air usage or loss is equal to or greater than the compressor’s output.
• Faulty Pressure Switch: The issue lies in the fact that the switch responsible for detecting system pressure isn’t sending the “stop” signal.
• Unloader Valve Malfunction: The valve that stops the compression cycle is stuck or has failed.

Safe DIY Checks You Can Carry Out

1. The Isolation Test: Close the main outlet valve on the air receiver tank.
2. Observe the Result:
   • Scenario A: The compressor builds pressure and shuts off. The problem is a large air leak or high demand in your plant.
   • Scenario B: The compressor continues to run. If it runs past its setpoint, the safety valve will release pressure. This indicates a fault in the control system.

When You Should Contact a Professional Engineer

• The isolation test points to a control system fault. The machine should be shut down.
• The safety relief valve activates. This indicates a critical failure of the primary controls.

From Reactive to Proactive: Preventative Maintenance

The causes of the majority of these typical air compressor failures are related to the lack of the performance of simple routine maintenance. The best way to maintain reliability is to move from a reactive to a preventive maintenance strategy. Understanding Why Regular Air Compressor Servicing is Important is the very first step in developing a preventive maintenance strategy. A carefully thought-out maintenance schedule will keep your system operating effectively and in accordance with safety standards.

Conclusion

A vital component of your operation is a reliable compressed air system. Understanding these seven common issues empowers your team to perform effective first-line maintenance. For complex diagnostics, internal repairs, or managing your legal safety obligations, partnering with a specialist provider is essential. A dependable system is an essential component of How to Make Your Air Compressor More Efficient, minimising energy and downtime costs.

For out of hours emergency call outs in Cardiff, Newport, Swansea, Bristol, Gloucester and nearby areas, we have engineers available 24 hours a day.

For information on a preventative maintenance schedule and PSSR compliance, contact our service team today.