There is a correct order to diagnose a pool robot, and it is not the order most people use. Most people start by suspecting the expensive component. The right order starts with the free checks, because the free checks are also the most likely causes.
The free five, in order
- Empty and rinse the filter. A blinded filter causes low pickup, failed wall climbing, motor-overload errors and short runtimes — four different-looking symptoms with one cause.
- Clear the intake and impeller housing. A leaf plug in the throat is invisible from outside and stops the machine collecting anything.
- Check every rotating shaft for a wrap. Pine needles, hair and grass wrap brush and wheel axles and load the drive motor continuously.
- Look at the brushes. Flat equals no grip. This is the wall-climbing answer.
- Check the water level. Low level breaks skimming, waterline cleaning, and on some machines triggers a fault.
Symptom to cause, at a glance
| Symptom | Most likely cause | Fix |
|---|
| Picks up almost nothing | Blinded filter or blocked intake | Free — rinse and clear |
| Stopped climbing walls | Worn front brush, then worn tracks | ~$23-35 |
| Will not charge at all | Failed charger, then corroded contacts | ~$10-17 |
| Runs 40 min where it used to run 2 h | Degraded battery — normal ageing | ~$70-80 where a pack exists |
| Keeps stopping mid-cycle | Motor overload from a blockage or wrap | Free |
| Gets stuck in the same spot | Drain, step return or a floor seam | Free — reposition start point |
| Misses the same area every cycle | Pool exceeds its rated area, or pattern navigation | Run more cycles, or the wrong machine |
| Pushes sand around | Filter coarser than the debris | Fine filter, ~$19-33 |
| Leaves a clean floor and a dirty cove | No edge-biased brush coverage | Manual brushing, or an edge-focused machine |
The faults that need a part, and which part
Wall climbing → brushes and tracks. Charging → charger, then battery. Suction genuinely gone with a clean filter → the pump motor and impeller assembly, which on a Dolphin is about $110 and is a real repair rather than a replacement. Low flow on a fine filter → the filter is doing its job; rinse after every run or step up to a staged coarse-over-fine design.
The faults that mean stop
Water inside the housing, a burning smell, a swollen battery pack, or a damaged cable on a corded machine. None of those is a home repair. Water ingress in particular will destroy the motor and electronics if you keep running it, and a damaged low-voltage cable in a pool is a safety matter — see Pool Safely.
Preventive maintenance that eliminates most of this
- Empty and rinse the filter after every cycle, while it is wet.
- Check brush and wheel axles for wraps weekly in leaf and needle season.
- Rinse grit out of tracks and bearings, especially on pebble pools.
- Keep it out of direct sun between runs — UV embrittles the shell faster than chlorine.
- Store a cordless pack at half charge, indoors, above freezing, over winter. This single habit prevents the most expensive common failure.
- Replace brushes before they go flat rather than after. The brush section has the part numbers.
