The massage that could still dissolve stiff shoulders last summer now feels like a lukewarm fizz. The good news: in most cases the pump is not to blame — it is a closed ring on a jet, a low water level or a clogged filter — in other words, things you can sort out in ten minutes and for nothing. The procedure below runs from the cheapest cause to the most expensive, so you only reach the costly scenarios once the cheap ones have failed.
First work out what is actually happening
Before you reach for tools, describe the problem precisely. The difference between “all the jets are weak”, “only one is weak” and “water flows but there are no bubbles” sends you to a completely different circuit of the hot tub — and saves you an hour of pointless searching.
A hot tub has three independent systems: the water circuit (pump, filter, pipework), the air circuit (blower or air drawn into the jet) and the controls (the control pack with its operating modes). The symptom tells you which one to inspect.
| Symptom | Most likely circuit | Where to start looking |
|---|---|---|
| All the jets are weak at once | Water circuit, suction | Water level, filter, suction basket, air lock |
| Only one jet is weak | The jet itself | Rotating ring, limescale, inside of the jet |
| Only some jets are strong, the rest do nothing | Diverter valve | Rotary knob on the rim of the shell |
| Water flows but there are no bubbles | Air circuit | Air control, blower, blocked air intake |
| The jets fade gradually over weeks | Filtration or deposits | Filter, limescale, biofilm in the pipework |
| The jets weakened right after a water change | Air in the pump | Air-locked pump, low water level |
| The pump hums differently, louder, or squeals | Pump | Impeller, bearings, cavitation |
1. A closed or throttled jet and the diverter valve
The most common “fault” that is no fault at all. Most hydromassage jets have a rotating outer ring — turning it anticlockwise opens the jet, clockwise closes it. All it takes is a back brushing against the ring, or a family member half-closing it, and the flow drops by half.
How to spot it: only one jet or a few jets are weak while the others run at full power. In fact the opposite often happens — closing a couple of jets boosts the remaining ones, so nobody notices the problem until a favourite spot goes weak.
The fix: try turning each jet both ways in turn and listen to how the sound of the flow changes. Then check the diverter valve — the large rotary knob on the rim of the shell that switches flow between groups of jets (typically seat versus lounger). In a mid position it splits the output in half and nothing has any real force. Turn it fully to one of its end positions. The air control works in much the same way: closed means a water flow with no bubbles and a noticeably softer massage. For an overview of which jets do what, see our article on types of hydromassage jets.
2. Low water level
The second thing to check before you take anything apart. The water level should reach roughly halfway up the skimmer, which on most hot tubs is a few centimetres above the highest jet. If it drops lower, the pump draws air instead of water through the skimmer and the output falls off a cliff.
How to spot it: the jets deliver an irregular, spluttering flow, you can hear slurping in the skimmer, and the level is below the mark. Typically after several days of bathing without topping up — in normal use, water carried out of the tub plus evaporation costs you a few centimetres a week.
The fix: top the water up. On a hot tub the level should be checked as routinely as the oil in a car, ideally once a week along with the water chemistry test. If the water is disappearing significantly faster than before, it is not evaporation and you should look for a leak.
3. A clogged filter — cause number one
Once you have ruled out the rings and the water level, start with the filter. A cartridge clogged with body oils, cosmetics and fibres is by far the most common reason a hot tub “loses its power” after a few months. The pump pushes water through the filter — a clogged filter is like breathing through a blanket.
How to spot it: jet power declined gradually over weeks or months, not overnight. The cartridge is greyish, greasy to the touch, and there are visible deposits between the pleats. Sometimes the chemistry becomes harder to hold at the same time and the water turns cloudy.
The fix: take the cartridge out and rinse between the individual pleats with a jet of water; every one to two months, soak it overnight in a degreasing filter cleaner. Rinsing with a hose alone will not remove oils — which is why a filter that looks clean can still be gummed up inside. Our guide to cleaning a hot tub filter covers the detailed procedure and the intervals. A cartridge lasts roughly 12–24 months; after two years, replace it regardless of how it looks.
4. A blocked suction basket or skimmer
Ahead of the filter there is usually a coarse suction basket or a suction grille on the floor or wall of the shell. A hair, a piece of plastic film from a bag, a leaf — and the flow is suddenly halved.
How to spot it: the flow dropped abruptly, often after bathing with children or after a windy day at an outdoor hot tub. Sometimes, with the jets switched off, you can see debris stuck directly to the grille.
The fix: switch the hot tub off at the main breaker, take the basket out, empty it and rinse it. Never remove the suction grille while the tub is running and never run the hot tub without it — suction safety covers are there to prevent hair entrapment and they are mandatory.
5. An air lock in the pump after a water change
The classic scenario: you drained the tub, filled it with fresh water, switched it on — and the jets barely flow at all. The pump is turning, but audibly “dry” or suspiciously quiet. Air is trapped in the pump body and a centrifugal pump cannot prime itself.
How to spot it: the problem appeared exactly after filling or after work on the pipework, and everything was fine before. The motor runs normally, but water either does not flow at all or only weakly.
The fix: switch the hot tub off at the breaker. Loosen the bleed screw on the pump body or its union, or carefully back off the union nut on the discharge side by a quarter turn until you feel air escape and water starts to seep out. Then tighten it and switch back on. Briefly running the jets on and off for a few seconds at a time also helps to push the air lock out. Never let the pump run dry for more than a few tens of seconds — without water the shaft seal is quickly damaged.
6. Jets clogged with limescale or biofilm
In hard water areas, scale builds up inside the jets and narrows the flow openings. On top of that, biofilm collects in the pipework and inside the jet bodies — a slime made of oils, cosmetics and bacteria that gradually reduces the bore.
How to spot it: one jet or a few jets are fading, with white crystals around their edges or, conversely, a slippery coating. The water may also foam or smell.
The fix: on most jets the internal part can be removed without tools. Turn the inner part anticlockwise by about a quarter turn and pull — on some types you first have to turn the jet all the way past the stop, where the bayonet lock “clicks”. Pull straight and do not lever; the plastic that has been through a winter of frost is the most brittle. Soak the removed internals overnight in a 1:1 vinegar and water solution or in a limescale remover, brush them with an old toothbrush and refit them. Regular hygiene prevents slime forming throughout the pipework, which is covered in our article on hot tub hygiene and legionella.
7. An air leak on the suction side — the pump is drawing air
This is where the more expensive half of the list begins. If there is a leaking union, a cracked nut or a dried-out seal somewhere on the suction side, the pump draws air instead of water. No water escapes anywhere — the vacuum pulls air in rather than pushing water out.
How to spot it: the flow from the jets contains irregular large bubbles even with the air control closed. The pump makes a crackling or “gravelly” noise — that is cavitation. In a clear pre-filter lid (if your hot tub has one) you can see that the water has not refilled to the top.
The fix: with the pump running, inspect every union on the suction side, hand-tighten them and check the O-rings. Replace any dried-out or flattened seal; these spare parts cost anything from a few euros to a few tens of euros. If you cannot find the leak, it is a job for a service engineer — prolonged cavitation destroys a pump.
8. A worn impeller or a failing pump
A hot tub pump typically lasts 5–10 years depending on use. The plastic impeller wears down, the bearings wear out and the output falls gradually, so owners often only notice after years.
How to spot it: the filter is clean, the level is fine, the suction is clear — and still the jets do not push. The motor runs, but it sounds different from before, louder or squealing. Sometimes the pump overheats and the thermal cut-out trips.
The fix: replacing the impeller is cheaper than replacing the whole pump, but it assumes the spare part is available. As a rough guide, budget around €100–200 for the part plus labour; for a complete pump replacement, more like €400 and up depending on the type. Our article on hot tub lifespan and servicing gives you the background for deciding between repair and replacement.
9. Control pack settings, economy and summer modes
Before you call a service engineer, open up the control panel. Many hot tubs have modes that deliberately limit operation — and while they are active the jets are simply not meant to run at full power.
Typically these are economy mode (heating and circulation only within a set window), sleep mode and, on some models, a summer mode that limits pump running in hot weather so the water does not overheat. Hot tubs with a two-speed pump also run on the circulation, i.e. slow, speed until you press the jets button — the high speed then has a time limit of 15 to 30 minutes and returns to the lower speed on its own once it expires. That is not a fault but a safeguard against a forgotten pump.
The fix: switch to standard mode and start the jets again with the button. If the panel behaves illogically or reports an error, check the error code list for your control system. Settings and timers on smarter models can also be checked from a phone — see controlling a hot tub from an app.
When a new jet or internal insert is all you need
Sometimes there is nothing to diagnose: a rotating jet stops spinning because its bearing is worn out, or a vane on the directional nozzle snaps off. Replacing the internal part of a jet is a matter of minutes and usually costs tens of euros, whereas the complete jet body is laminated into the structure of the shell and is only changed in exceptional cases during a major repair.
When buying a replacement, measure the outside diameter of the old jet and photograph it from the front and the side — jets are not interchangeable between brands and a difference of a few millimetres means the insert will not hold. Look for spare parts in our structural components and spare parts category.
When to call a service engineer
Home diagnosis ends where electrics and dismantled pipework begin. Call a service engineer if the pump’s thermal cut-out trips, if you can hear cavitation and cannot find the leak, if water is escaping from the equipment bay, or if the panel reports a repeated flow error even with a clean filter. Equally, there is no point experimenting on a hot tub that is still under warranty — unqualified work on the equipment can void it.
Prevention: three habits that keep the jets in shape
The vast majority of “pressure loss” originates in deferred maintenance. Three points are enough:
- Filter. Rinse every two to four weeks, chemical soak every one to two months, replacement after one to two years.
- Water level. Check once a week, top up to the middle of the skimmer. This prevents air locks and unnecessary strain on the pump.
- Chemistry. Balanced pH and hardness stop scale forming in the jets; you will find the step-by-step procedure in our article on hot tub water chemistry. For a year-round schedule of tasks, see the hot tub maintenance calendar.
Frequently asked questions
Why do the jets have power only briefly after switching on and then weaken?
Most often this is a two-speed pump returning to circulation speed once the timer expires. The other possibility is that a clogged filter “seals up” at the moment of higher flow and the flow rate drops — once the cartridge is cleaned, the problem disappears.
Can weak jets be a sign that it is time to change the water?
Indirectly, yes. Old water with a high level of dissolved solids clogs the filter faster and encourages slime to form. The replacement interval is covered in our article on how often to change hot tub water.
The jets are flowing but there are no bubbles at all. What now?
Check the air control on the rim of the shell to see whether it is closed, and on hot tubs with a blower, check its air intake, which tends to be hidden under the cabinet and readily blocks with leaves or insects. If the blower is not audibly running either, it is an electrical fault for a service engineer.
Will flushing the pipework help with weak jets?
Yes, if biofilm is the cause. A special pipe cleaner is dosed into the water, left to circulate, and then the tub is drained and rinsed out. The dirt that comes out is usually an unpleasant surprise — which is precisely why a flush is always done before a planned water change.
Can a freezing winter cause weak jets?
Indirectly. Water frozen in the pipework damages the jets, and plastic becomes brittle after seasons outdoors, so it snaps more easily. Operating and protecting a hot tub in frost is summarised in our article on hot tubs in winter.
Weak jets are, in the overwhelming majority of cases, a matter of fifteen minutes and zero cost — the ring, the level, the filter. Only once you have worked through the whole list and nothing has helped do you start dealing with the pump. And if your hot tub is old enough that a worn pump and brittle jets have arrived at the same time, it may make more sense to look for a new one: you will find the current range in our hot tubs category, and further guides in our Guide section.
