UPS troubleshooting: what you can check, what needs an engineer
When a UPS starts alarming, do not reach for the plug first. Reading what the panel is telling you is enough to judge whether it is something to watch — or something to deal with tonight.
Read the panel first, then draw a conclusion
Indicator lights and codes differ slightly from one UPS to another, but the causes cluster into a few groups. Below are the common symptoms and where to look:
| Symptom | Likely cause | Severity |
|---|---|---|
| Continuous alarm, equipment still running | Battery fault, overload, high internal temperature | Medium: test soon |
| Holds only a few seconds after an outage | Ageing battery string or a failed block | High: no real protection left |
| Frequently switching to battery while the mains is normal | Unstable mains voltage, loose input wiring, sensitivity set too high | Medium |
| Overload indicator permanently lit | Connected equipment exceeds capacity | High: shed load now |
| Over-temperature alarm, fans running at full speed | Blocked cooling path, high ambient temperature, fan failure | High: inspect cooling |
| Panel completely dead, will not start | Faulty input supply, internal fuse or power module failure | High: stop trying yourself |
| Transfer failure, output interrupted | Inverter module or bypass fault | High: needs professional repair |
Three things you can check yourself
- Shed load. Unplug all non-critical equipment (printers, heating appliances, unnecessary peripherals) and see whether the alarm stops.
- Look at the environment. Is the cabinet blocked around its vents? Is the room noticeably hot? Is there dust around the equipment?
- Check the input. Are the input socket and breaker loose or tripped? Is other equipment on the same circuit also misbehaving?
Carry out these three checks only when it is safe to do so, and do not open the enclosure.
When to call straight away
If any of the following is present, stop and contact us immediately:
- an unusual smell, abnormal heat, or a crackling or popping noise
- smoke, or a distorted casing
- a completely blank panel even though the input supply is confirmed present
- the UPS repeatedly switching on and off, or an obviously abnormal output voltage
- a battery string that is swollen, deformed, or leaking electrolyte
One important principle
"Wait until it breaks, then repair it" is the worst-value strategy for a UPS. Its faults tend to surface at the exact moment of an outage — which is precisely when you need it. Periodic testing, especially of battery internal resistance and capacity, finds problems before they fail, and that is far cheaper and safer than an emergency repair afterwards.
If you are unsure about the state of your system, we provide an on-site inspection and issue a report, after which you decide whether to replace anything — there is no obligation to order. Talk to us or see our services.