Troubleshooting a compressor that keeps shutting down starts with one split: did the machine trip instantly, or did its controller perform a managed shutdown? Instant trips point to electrical protection, while controlled shutdowns point to sensors, temperature, pressure, oil condition, or programmed self-protection.
For Birmingham and West Midlands sites, the cost is rarely just the stopped machine. Solihull spray booths, Tyseley fabrication lines, and packaging cells near the M6 corridor can lose the shift before anyone has found the fault.
J Ll Leach, Atlas Copco authorised distributor in the West Midlands, has supported compressed air systems since 1936 from Birmingham, Stoke and Shrewsbury. This guide walks through the checks we use before deciding whether the fault is thermal, electrical, mechanical, control-related, or compliance-critical.
Trip or Shutdown: Start With the Evidence
A trip is an instant protective stop. A shutdown is a controlled stop triggered by a sensor, PLC, or controller. It happens when temperature, current, pressure, or oil pressure moves outside safe limits.
That distinction tells you whether to start with the electrical supply or the machine’s logged operating data.
Modern industrial units protect themselves. PLCs and controllers will halt the machine if internal temperature, oil pressure, discharge pressure, or electrical current moves beyond safe limits.
Fault Codes Matter
Code evidence matters. Code F21 (Motor Overload) confirms that the thermal relay has tripped due to excessive current, which is different from a general high-temperature shutdown.
If the same code returns after a reset, treat the fault as active. Repeated resets can turn a simple overload or cooling issue into a damaged motor, contactor, or airend.
What to Check First
Where a circuit breaker keeps opening, the issue may sit upstream of the machine. Our guide to why your compressor keeps blowing the fuse or breaker covers that electrical route in more depth.
A controller log narrows the fault quickly, but safety rules decide how far the in-house team should go. If the unit has stopped more than once, write down the exact alarm, the pressure reading, the room temperature, and what production process was running.
Safety and Compliance Come Before Resetting
Compressed air is stored energy, not just workshop utility air. The Pressure Systems Safety Regulations 2000 apply to compressed air systems above 0.5 bar, and a Written Scheme of Examination is required when pressure multiplied by volume exceeds 250 bar-litres.
The Pressure Systems Safety Regulations 2000 guidance (hse.gov.uk) applies to systems containing a relevant fluid at more than 0.5 bar above atmospheric pressure. Compressed air is included.
If your receiver is 150 litres and runs at 10 bar, that’s 1,500 bar-litres. It’s well above the 250 bar-litre threshold, so it legally needs a Written Scheme of Examination.
Written Scheme Basics
A WSE is a legal inspection plan. It identifies pressure vessels, significant pipework, and protective devices, then states the nature and frequency of examination.
It should cover:
- The receiver and any other pressure vessel.
- Significant pipework exposed to stored pressure.
- Protective devices, including the safety valve.
- Examination intervals and inspection scope.
- The competent person responsible for examination.
Maintenance Duties
Non-compliance can mean severe injury, forced operational halts, fines, and personal liability for company directors. That’s why troubleshooting is never just an uptime task.
PUWER, the Provision and Use of Work Equipment Regulations 1998, adds another duty. Work equipment must be suitable for its intended use, safe to operate, and maintained in safe condition.
Why Isolation Matters
The regulator’s HSG39 compressed air safety guidance (hse.gov.uk) highlights the dangers of stored pressure, including violent overpressurisation, fire risk, and bodily harm from uncontrolled discharge. Overpressurisation can follow blocked outlets, failed automatic controls, or external heat.
Physical harm can include skin penetration, eye injury from particles, and air entering the body. When a unit stops due to overheating or pressure anomalies, HSG39 advises safe isolation, interlocking methods, and tamper-resistant pressure regulators during the troubleshooting process.
That means depressurise, lock off, and prove zero stored energy before removing guards or opening pressure components. BCAS guidance also matters here.
Competence and Limits
BPG 101-6 and BPG 102 are useful references when site teams review safe compressed air operation, competent maintenance, pressure system responsibilities, and the limits of what should be handled internally.
Once the site is safe, the fault log and temperature history tell you whether heat has been building for hours.
Thermal Issues: Overheating Is the Common Shutdown Route
Overheating is one of the most common reasons an industrial machine stops under load. On many Atlas Copco GA series units, high-temperature warnings appear at about 110°C, with hard shutdown around 120°C to protect internal airend components.
Heat is the by-product of compression. Avelair’s maintenance research notes that about 90% of electrical energy becomes heat. Only around 10% converts into compressed air.
If the plant room is hot, that heat has nowhere to go. The machine starts ingesting its own exhaust air, and the fault repeats every time demand rises.
The Heat Fault Checklist
High ambient temperature and poor ventilation are common in cramped West Midlands plant rooms. We see it in Aston, Small Heath, and older Black Country units where production has expanded but the plant room hasn’t.
The pattern matters because heat faults rarely arrive alone. A dirty cooler can raise oil temperature, increase current draw, shorten separator life, and make a motor overload fault appear after the first reset.
Cooling and Oil Checks
If coolers are clogged, airflow through the fins drops. In dusty fabrication shops, the debris can form a blanket over the cooler face.
Professional chemical cleaning may be needed for heavily clogged coolers. Blowing the surface with an airline won’t clear baked-in contamination.
Low oil levels stop heat moving away from the airend. Top up only with manufacturer-specified synthetic or mineral oil, and don’t mix oil types unless the manufacturer permits it.
When Heat Becomes a Chain Fault
Thermal faults become expensive when the drive system has to work harder against heat, friction, or restriction. They also shorten oil life, damage seals, increase separator pressure drop, and turn a simple service issue into a stoppage that affects production.
Motor Overload, Voltage and Drive Faults
Motor overload means the machine is drawing more current than it should. It may be caused by mechanical binding, failing bearings, an electrical short in stator windings, voltage instability, or a drive fault that stops the unit before damage spreads.
An immediate trip is different from a slow heat build-up. If Code F21 appears, the motor overload relay has detected excessive current and opened the protection circuit.
That’s a protective action. Don’t uprate the device to keep the plant running, because the next failure may be the winding, contactor, or airend.
Electrical Fault Pattern
Atlas Copco troubleshooting references include phase sequence and voltage instability faults. A wrong phase sequence on a 3-phase supply can make the machine run backwards, risking immediate airend damage.
Electrical faults should be logged as a pattern, not treated as isolated events. If the same unit trips at start-up on Monday mornings but runs after lunch, the fault may involve damp, low temperature, start components, or supply quality rather than one failed motor.
Capacitors, Drives and Supply Quality
On single-phase units, start or run capacitors should be discharged and tested with a multimeter. Replace them when capacitance is outside tolerance.
A variable speed drive is sensitive to heat, voltage quality, and cooling airflow. Dust in the cabinet can trigger drive protection even when the airend is sound.
If you’re comparing electrical symptoms against mechanical ones, belts are a useful dividing line. The air compressor belt care guide explains how slip, chirping, and tension faults show up before a shutdown.
When Load Creates Electrical Symptoms
Electrical protection often exposes the load problem, and the load often comes from the air system downstream. If demand has risen, pipework is restricted, or the machine is being forced above its proper duty pattern, the overload device may be reporting the consequence rather than the original cause.
Pressure Switch, Unloader and Control Faults
If a unit starts, builds pressure, then stops or refuses to restart, the pressure switch, unloader valve, sensing line, or controller logic may be at fault. These parts control when the machine loads, unloads, stops, and restarts under safe conditions.
A pressure switch fault can mimic a major mechanical issue. The contacts may open too early, fail to close, or respond to a blocked sensing line rather than receiver pressure.
On rotary screw compressor installations, the control sequence is more involved. The machine may unload, wait, restart, or alarm depending on demand and programmed limits.
Control Checks That Save Time
- Confirm the cut-in and cut-out settings against the site requirement.
- Check whether the receiver gauge matches controller pressure.
- Inspect the sensing line for blockage, water, or oil contamination.
- Confirm the unloader moves freely and vents correctly.
- Read the fault history before clearing alarms.
If the machine stops before reaching pressure, don’t assume the pump is weak. A blocked inlet filter, unloading fault, or downstream restriction can make the controller respond as if the system is unsafe.
The useful question is whether the pressure reading is real. Compare the controller display, receiver gauge, and downstream gauge before changing pressure settings.
Low Pressure and Shutdown Loops
Low plant pressure can be a symptom, not the main fault. A unit may run flat out, overheat, and stop because the network has leaks or the demand has outgrown the installed capacity.
The same applies where pipework is undersized. British Compressed Air Society installation guidance addresses reliability, noting that wrong equipment selection or poor pipework design can cause pressure drops, supply issues, and frequent downtime.
If pressure keeps falling before the stop, read our guide to low pressure from your air compressor. That route usually starts with leaks, storage, pipe diameter, and demand profiling.
When Controls Read the Wrong Pressure
When control faults repeat, the next question is whether the air itself is contaminating the system. Moisture, oil carryover, and debris can block sensing lines, make valves stick, and create pressure readings that no longer reflect what is happening in the receiver or ring main.
Filtration, Moisture and Air Quality Faults
Compressed air carries water, oil, and particles unless treatment is specified and maintained correctly. Poor filtration and condensate control can block valves, seize pneumatic components, increase pressure drop, and force the system into repeated fault states.
British Compressed Air Society guidance is anchored in the ISO 8573 standard series, which defines purity classes for particles, water, and oil aerosols or vapours. That matters in food, paint, medical, and precision manufacturing work.
Breathing-air and specialist process applications need a different level of control. BS EN 12021 and EN 12021 are commonly referenced for breathing air quality, while general factory air should still be specified against the purity class the process actually needs.
Air Treatment Fault Table
BCAS BPG 104 covers filtration and drying. It explains why air treatment must match the application, not just the pipe size.
Moisture is often the hidden fault. Excess water vapour can create microbial hot spots, corrosion, blocked valves, and sticky controls that make the compressor look unreliable when the real issue sits downstream.
Condensate and Blocked Components
In a Birmingham bodyshop, a small amount of oil or water in the line can ruin a paint finish. In food production, purity class and condensate control become quality issues as well as maintenance issues.
Replacement filters and service kits are available from our online shop, usually dispatched the same day from our Birmingham warehouse. Order direct if you have an in-house engineer and know the part reference.
If filters are changed but shutdowns continue, the cause may sit in system design rather than one failed component.
Installation, Pipework and Demand Mismatch
A machine that’s too small, badly sited, or connected to poor pipework will keep stopping because it’s being asked to solve a system fault. BCAS installation guidance warns that wrong equipment selection and poor pipework design can cause pressure drops, supply problems, and frequent downtime.
We see this when production grows around an old installation. A unit that once fed a few tools now feeds spray booths, CNC equipment, packaging machinery, and open-ended leaks.
Duty cycle matters too. A 50% duty cycle means the machine can run for 5 minutes in every 10 before it needs cooling time.
When the System Is the Fault
In a Tyseley metalworking unit, this often looks like a machine that’s fine at 6am but fails by mid-morning. Demand rises, room temperature rises, and the system has no margin left.
A leak survey can use an acoustic method, especially ultrasonic leak detection, to find waste that is hard to hear during production. That evidence helps separate a weak machine from a network that’s losing air faster than the plant can make it.
Testing and Pressure Work
BCAS BPG 103 covers pressure and leak testing. It recommends small, safe steps for pneumatic testing and warns against hydraulic water testing on air systems because internal rust can follow.
For a 75 kW installation, ventilation design can require airflow in the region of 20,000 to 22,000 m³/h. That figure alone explains why putting the machine in a sealed corner is asking for trouble.
When the root cause is demand, prediction beats repeated repair.
Predictive Maintenance and 2026 Fault Prevention
The industry is shifting from reactive maintenance to predictive maintenance, with IoT-enabled diagnostics and AI-supported fault trend analysis expected to shape good practice through 2026. For maintenance teams, that means fewer surprise stops and better evidence before authorising repair spend.
Europe-wide IoT adoption in industrial compressed air is reported at around 45%. The direction is clear: more sites want controller data, running-hour trends, temperature history, and energy data before a failure.
That doesn’t replace engineering judgement. It gives the engineer better evidence before opening the machine.
What We Track on Service Visits
- Running hours, loaded hours, and off-load behaviour.
- Discharge temperature and warning history.
- Oil condition, oil filter status, and separator pressure drop.
- Cooling airflow and cabinet temperature.
- Receiver pressure stability and network demand.
- Alarm codes, including motor overload and inverter trips.
Trend Data Between Visits
Energy should be part of the same discussion. Over a machine’s lifetime, energy can account for more than 70% of total ownership cost, and poorly controlled off-load running wastes power without making useful air.
Remote monitoring is the trend that makes this practical between service visits. Temperature drift, separator pressure drop, load hours, and repeated resets can be reviewed before the next planned maintenance date.
Internet of Things and IIoT monitoring add value when they support preventive maintenance rather than just another dashboard. Vibration monitoring, oil sampling, and ultrasound checks can show bearing wear, lubricant breakdown, and leak loss before a controller reaches a hard shutdown. The value is trend evidence, not clever labels.
Vibration, Bearings and Early Warnings
Mechanical condition checks also have standards behind them. ISO 20816 is widely used for vibration evaluation on rotating machinery, while ISO 13373 supports condition monitoring and vibration diagnostics.
A rising vibration trend can point to bearing wear, coupling issues, imbalance, belt problems, or airend distress before the controller reaches a hard shutdown. Used alongside oil analysis and temperature history, it can stop the same fault being reset until the expensive part fails.
These checks are most useful when readings are compared against a baseline. A one-off vibration number helps, but trend evidence shows whether the machine is stable, deteriorating slowly, or moving quickly toward failure.
Birmingham Service Scenario
A bodyshop near Castle Bromwich calls at 7am. The unit has stopped twice before the first booth run, and the controller shows a high-temperature fault followed by F21 after reset.
Our engineer checks the cooler, intake path, oil level, cabinet fan, and current draw before clearing the alarm. If the cooler is blocked and the overload relay has tripped under rising load, resetting without cleaning only restarts the failure.
For local sites, the advantage is stock and response. We can leave the Cuckoo Road depot with filters, belts, sensors, and common Atlas Copco service parts rather than waiting for a courier.
Fix the Cause, Not the Alarm
The practical difference is between getting the unit running and protecting the shift. A clean fault trail lets the engineer bring the right parts, check the right system, and avoid repeating a reset that was never going to hold.
It also helps the production manager make a better call. If the cause is a blocked cooler, the repair route is different from an undersized ring main, a failed drive fan, or a receiver that needs inspection under the Written Scheme.
Frequently Asked Questions
The answers below cover the faults we’re asked about most often during callouts across Birmingham, the Black Country, Coventry, and Staffordshire.
Why Does My Compressor Keep Shutting Down?
Your unit keeps shutting down because a protection device or controller has detected unsafe operation. Common causes include overheating, low oil levels, blocked coolers, pressure control faults, electrical overload, poor ventilation, or excessive demand. Check the fault code first, isolate safely, then trace the system condition that triggered the stop.
What Are the Symptoms of a Faulty Unloader Valve on an Air Compressor?
A faulty unloader valve can cause hard starting, repeated trips, pressure trapped in the discharge line, slow pressure recovery, or a machine that starts then stops quickly. You may hear air venting at the wrong time. On larger systems, the controller may log loading or pressure faults.
Why Won’t My Air Compressor Stay Running?
A machine that won’t stay running is usually reacting to an active fault rather than failing at random. Check the controller log, inlet restriction, cooling airflow, oil level, pressure setting, and electrical supply. If it stops under load, suspect overheating, overload current, airend load, or downstream pressure restriction.
How Do I Reset a Compressor?
Reset only after the fault has been identified and made safe. Isolate the unit, allow temperature and pressure to return to safe levels, check the logged alarm, then follow the manufacturer’s reset sequence on the controller. If the same fault returns, stop resetting and call an engineer.
When Does an Air System Need a Written Scheme of Examination?
A Written Scheme of Examination is required when operating pressure in bar multiplied by internal volume in litres exceeds 250 bar-litres. PSSR 2000 applies above 0.5 bar for relevant fluids including compressed air. A competent person must define the inspection scope, frequency, and safety devices covered.
Should I Call an Engineer for Code F21?
Yes, if Code F21 returns after one safe reset. F21 confirms motor overload, meaning excessive current has tripped the thermal protection. The cause may be electrical, mechanical, or load-related.
An engineer should test current draw, bearings, supply voltage, cooling, and controller history before restart.
If your compressor is shutting down and the fault keeps returning, call J Ll Leach in Birmingham on 0121 773 5630. Tell us the fault code, the machine model, and what was running when it stopped, and we’ll prioritise the right engineer and parts for the callout.