Most cooling tower problems announce themselves the same few ways: the water is not cold enough, the water bill has gone up, something is making a noise it did not used to make, or the fan has stopped.
Work through the symptom you are seeing below. Each section lists the likely causes in the order worth checking, and links to the fix.
If you would rather talk it through, call us on 800-752-1905. We have been building these towers since 1971 and we can usually narrow it down in a few minutes.
Before you start
Shut down and lock out the fan motor and the circulating pump before anyone goes inside a tower, on top of one, or reaches into the basin. Cooling towers combine moving parts, standing water and live electrical connections in a confined space.
Take a few notes while you work. When the problem started, whether it appeared suddenly or came on gradually, and what has changed recently — new equipment on the loop, a change in operating hours, a water treatment change. Sudden problems and gradual problems have different causes, and knowing which you have narrows the list immediately.
The water is not cooling enough
The most common complaint, and it has several possible causes. Check in this order:
1. Fouled or collapsed fill
The usual culprit, particularly when the problem has come on gradually over months or years. Fill is where heat transfer happens, and scale, biological growth, or physical collapse all reduce it. Open the tower and look at the fill surfaces and flute passages.
How to inspect fill and decide whether to clean or replace it
2. Blocked or missing spray nozzles
Nozzles distribute water evenly across the fill. When they clog, sections of fill run dry and stop contributing to cooling — you can lose a significant share of capacity to a handful of blocked nozzles. Run the tower and look at the distribution pattern from above. It should be even across the full area, with no dry patches or concentrated streams.
3. Reduced airflow
Confirm the fan is turning at full speed and in the correct direction, the blades are set to the right pitch, and the air inlet louvers are clear of debris. A fan running backwards moves a fraction of the air it should, and it is a surprisingly common finding after electrical work has been done on a site.
Motor and drive troubleshooting
4. The heat load has increased
Has equipment been added to the loop since the tower was installed? A tower sized correctly five years ago may simply be undersized for today's load. This is worth checking before you spend money on parts, because no amount of maintenance fixes an undersized tower.
Check what capacity you actually need
5. High ambient wet bulb temperature
A cooling tower cannot cool water below the ambient wet bulb temperature, no matter how large or how clean it is. On unusually humid days, warmer leaving water is physics rather than a fault. Compare current conditions against the design wet bulb the tower was selected for before assuming something is broken — our wet bulb guide lists design conditions by city.
6. Water flow rate is wrong
Too much flow and water passes through the fill too quickly to give up its heat. Too little and distribution suffers. Check the pump, any bypass valves, and whether anything has changed in the piping.
7. Scaling in the distribution system
Scale builds in the distribution piping and headers as well as on the fill, restricting flow before the water ever reaches the nozzles.
Excessive water loss or drift
Some water loss is normal and unavoidable — evaporation is how a cooling tower works. A tower rejecting heat will always consume makeup water. The question is whether consumption has risen beyond what evaporation explains.
- Failed drift eliminators — water droplets escaping with the exhaust air rather than being captured and returned. Visible as mist or spray above the tower, and it means you are losing treated water to the atmosphere.
- Basin overflow — usually a stuck, misadjusted, or worn float valve. Cheap to fix and easy to miss.
- Excessive bleed rate — check your water treatment settings. An over-aggressive bleed wastes both water and chemical.
- Leaks — basin, piping connections, or a cracked shell panel
- Splash-out — water escaping through the air inlets, often from over-pumping or a distribution problem
Drift eliminators, float valves and basin hardware
Unusual noise
| What you hear | Likely cause |
|---|---|
| Grinding or rumbling | Motor or fan shaft bearings |
| Squealing on startup | Belt slip, on belt drive models |
| Rhythmic knocking | Fan blade contacting the shroud, or a loose blade |
| Humming with no rotation | Seized bearing, lost phase, or failed capacitor |
| Rattling | Loose hardware, panel, or louver |
| Louder water noise than usual | Changed water distribution — check nozzles |
| Hissing or spraying | Leak in the distribution piping |
Noise that develops gradually usually means wear. Noise that appears suddenly usually means something has broken or come loose, and warrants shutting down to look before running further.
Vibration
Vibration destroys bearings, loosens structural connections and fasteners, and in extreme cases damages the tower structure. Do not leave a vibrating tower running while you decide what to do about it.
- Fan imbalance — the most common cause by a wide margin. Debris stuck to one blade, a damaged or eroded blade, or ice buildup in winter operation.
- Incorrect or uneven blade pitch — every blade must be set to the same pitch. A single blade out of adjustment unbalances the whole assembly.
- Worn bearings — motor or fan shaft
- Sheave misalignment on belt drive models
- Loose mounting hardware — motor mounts, fan deck fasteners, structural connections
- A bent shaft — usually from a previous impact or seizure
If vibration appears suddenly, shut the tower down and inspect the fan before running it again. A blade that has come loose at speed is dangerous.
Algae, slime, or scale
Recirculating water concentrates dissolved minerals and provides warm, oxygenated, sunlit conditions that biological growth thrives in. This is a water treatment issue rather than an equipment fault — but it causes equipment faults if it is left alone.
- Green or brown slime — biological growth. Check the biocide program and dosing.
- White chalky deposits — mineral scale. Check bleed rate and cycles of concentration against your makeup water hardness.
- Growth concentrated in one area — often where sunlight is reaching the basin or fill through a missing louver or panel
- Rapid regrowth after cleaning — the treatment program is not keeping up
Left untreated, fouling blocks the fill, clogs the nozzles, restricts airflow and reduces capacity — which brings you back to the first section of this page. Fix the water chemistry before replacing parts, or you will replace them again.
Leaks
- Basin leaks — on a galvanized steel tower this usually means corrosion has perforated the basin, and it is often the point at which repair stops making sense. On an FRP tower, check for impact damage or a failed seal, both of which are repairable.
- Piping connections — gaskets, threaded fittings, and flange bolts
- Cracked shell or panel — impact, freeze damage, or age
- Distribution piping — inside the tower, often only visible with the fan off and the pump running
A corroding basin on a steel tower is the classic end-of-life indicator. By the time it is visible from outside, the metal is usually further gone than it looks.
Why FRP towers do not have this failure mode
Fan will not start
- Check the disconnect and the breaker
- Check the overload — if it has tripped, find out why before resetting it
- Check voltage at the motor terminals on all three phases, under load
- Check the starter and contactor for pitted or welded contacts
- Check the junction box for moisture and corroded connections
- With power locked out, turn the fan by hand — resistance or grinding means a seized bearing
Freezing problems in winter
Towers operating through freezing weather need particular attention:
- Ice on the fill or louvers — restricts airflow and adds weight the structure was not designed to carry
- Basin freezing — check that basin heaters are working before the first cold snap, not after
- Ice on fan blades — causes severe imbalance and vibration
We supply immersion heaters and basin heater kits for winterization. Check them at the start of each cold season.
Recommended inspection schedule
[CONFIRM WITH CTS: replace these intervals with their official service recommendations. The Operating Instructions & Service Manual may already contain them.]
Monthly
- Water level in the basin
- Visible drift from the top of the tower
- Debris in the basin and strainer
- Any change in sound or vibration
- General visual inspection of the structure
Quarterly
- Fill condition and fouling
- Spray nozzles and water distribution pattern
- Belt tension and condition, on belt drive models
- Float valve operation
- Louver condition and cleanliness
Annually
- Motor amp draw measured against nameplate rating
- Fan blades, pitch and balance
- Drift eliminator condition
- Basin and structural inspection
- Full cleaning
- Electrical connections and junction box
Full detail is in the Operating Instructions & Service Manual.
Repair or replace?
A reasonable guide: if the parts needed exceed roughly half the cost of a new tower, or if the structure itself is failing, replacement usually makes more sense than repair.
Signs a tower has reached the end of its useful life:
- Basin or shell corroded through
- Structural members failing or visibly deflecting
- Multiple major components due at once — fill, motor, drift eliminators, distribution
- Capacity no longer meets the load even in good condition
- Parts no longer available for the make and model
- Repeated failures of the same component with no identifiable external cause
We will tell you honestly which side of that line you are on. We would rather sell you a motor than a tower you do not need.
Still not sure?
Send us the symptom, your model number, and a photo if you have one. We will tell you what is likely wrong and what it takes to fix it.
Contact us or call 800-752-1905. No voicemail — you will speak to someone who knows the product.
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