Spa Pump Hums But Won’t Start: What to Check First

Why does a spa pump hum but not start?

A spa pump that hums but won’t start almost always has one of three faults: a failed run capacitor, a seized shaft, or a jammed impeller. The hum means the motor is getting 230V power but cannot create the rotating magnetic field it needs to turn, and in a single-phase spa pump, that field comes from the run capacitor. Capacitor failure is the most common of the three, especially after a pump has sat idle over winter. To narrow it down: isolate the power, discharge the capacitor, then try turning the motor shaft by hand from the fan end. If the shaft spins freely, suspect the capacitor: test it with a multimeter on capacitance mode and replace it if it reads outside ±5% of the µF value printed on the label. If the shaft won’t turn, the pump is seized and a new capacitor won’t fix it.

That hum, by the way, is the sound of NZ’s 230V/50Hz mains vibrating a stalled winding: the motor is energised, just not rotating. Don’t keep jabbing the start button while you diagnose: a stalled motor draws locked-rotor current, several times its normal running current, and that heat goes straight into the windings.

Is it the capacitor, the controller, or the pump itself?

Spa systems have a controller or spa pack between the power and the motor, but the hum itself does half the diagnosis for you:

1. No hum, no sound at all? The motor isn’t getting power, check for a tripped RCD at the switchboard, a controller fault, or a blown fuse in the spa pack. Reset a tripped RCD once; if it trips again, stop and call an electrician.
2. Pump hums? Power is reaching the motor, so the controller has done its job. The fault is in the pump itself.
3. Isolate the power, discharge the capacitor, then turn the shaft by hand at the fan end. Spas idle through winter are prime candidates for a stuck mechanical seal: the faces bond together after months without running.
4. Shaft spins freely? Suspect the capacitor. Test it (next section).
5. Shaft won’t turn? The pump is seized: stuck seal faces, corroded bearings, or debris in the impeller. A firm turn by hand often frees a stuck seal; complete lock-up points to bearings.

Two-speed spa pumps such as Davey’s QB2002, QB2502 and QB3002 list a single run capacitor in Davey’s parts catalogue, so a dead capacitor stops the pump on high and low. If it runs on one speed but hums on the other, look at the controller relay or the speed winding instead.

How do you confirm the capacitor is dead?

You need a multimeter with a capacitance (F/µF) mode. Many inexpensive meters include one. Then:

1. Isolate the power: unplug the pump, or switch off the spa’s isolator and breaker.
2. Open the capacitor cover, usually a hump or end-cap on the motor casing.
3. Discharge the capacitor across both terminals with a bleed resistor or discharge tool.
4. Read the label: for example “12µF ±5% 450VAC”. A healthy 12µF capacitor measures roughly 11.4-12.6µF.
5. Disconnect the leads and measure across the terminals on capacitance mode.
6. Replace it if it reads outside ±5% of the printed value, reads open (OL), or shows any physical damage: bulged top, split case, or oily residue.

The full walkthrough is in our guide to testing a pump capacitor with a multimeter.

What size capacitor does your spa pump take?

The source of truth is the label on your existing capacitor: match the µF on the label (within ±5% is fine), and use the same or a higher voltage (450V replaces 400V or 440V). But it helps to know what the manufacturer fitted, especially if your label has cooked beyond reading.

These values come from Davey’s published parts documentation for its spa and spa-bath ranges, the same fitment data behind our Davey capacitor finder:

Davey model	System	OEM capacitor	Voltage
Celsior C200 (C200A/AB/TB)	Spa bath	8µF	450V
Spa Bath T/JET 170 (56221/56231)	Spa bath, heated	8µF	450V
Celsior C270 (C270A/AB/TB)	Spa bath	12µF	450V
Spa Bath T/JET 230 (56221/56231)	Spa bath, heated	12µF	450V
Spa Bath XS200/XS250/XS300 (76xxx)	Spa bath, heated	12µF	450V
XS Series (XS250/300, HG/HF/HSP)	Spa pool circulation	12µF	450V
Celsior C400 (C400A/AB/TB)	Spa bath	25µF	450V
Storm 150M	Spa pool circulation	25µF	450V
Storm 200M	Spa pool circulation	30µF	450V
QB2001 / QB2002	Spa pool, 1 & 2 speed	30µF	450V
QB2501 / QB2502 / QB3001 / QB3002	Spa pool, 1 & 2 speed	40µF	450V

All of these are CBB60-type run capacitors. Where Davey’s parts list prints only a µF value, the 450V shown is the standard replacement rating, equal to or higher than anything originally fitted. Treat the table as a starting point, not a guarantee. Manufacturers change motors between production runs, so always confirm against the µF and voltage printed on your own capacitor before ordering. The Davey capacitor finder has the full model list, and for other brands (Onga, Bianco, DAB, Grundfos) the capacitor wizard walks you through matching from the label. A 12µF 450V CBB60, the most common spa-bath value above, costs from NZ$24.95.

Can you replace a spa pump capacitor yourself?

It depends on how the pump is connected. A spa-bath pump under an acrylic bath normally plugs into a socket: unplug it, discharge the capacitor, and fit a replacement that matches the µF on the label (within ±5% is fine) with the same or a higher voltage rating. An outdoor spa-pool pump is usually wired into the spa controller rather than plugged in. Look at the connection before you start. A plug and socket means you can unplug it and work on it safely; a cable running into conduit, a wall or a control box means the circuit has to be isolated at the switchboard first. If you’re not confident working on mains equipment, have a registered electrician do it.

If your pump is the plug-in kind, the swap itself is a 15-minute job with a screwdriver: the spa pump capacitor replacement guide covers it step by step.

What if the spa pump still hums with a new capacitor?

A new capacitor fixes the most common cause, not every cause. If the hum persists:

1. Re-check the shaft. With power isolated, it should spin freely by hand. Stiff or locked means seized bearings or a stuck seal.
2. Check the impeller. Debris, scale or a broken seal spring can jam it. On most spa pumps the wet end pulls off the motor without disturbing the plumbing.
3. Confirm the spec. A capacitor well below the required µF value (say a 12µF fitted where 25µF belongs) may hum or start weakly. Match the label, not a guess.
4. Let the thermal cut-out reset. A motor that has been humming repeatedly may be too hot to restart. Leave it off for an hour, then try once.
5. Suspect the windings. If the shaft is free and the capacitor is new and correct, the start winding may be open or burnt. Get a professional diagnosis before spending more.

Frequently asked questions

Can I use a higher µF capacitor in my spa pump?

No. Match the µF on the label; within ±5% is fine. A noticeably higher value pushes more current through the auxiliary winding and overheats it. The voltage rating is the one you can go up on: a 450V capacitor safely replaces a 400V or 440V original of the same µF.

My two-speed spa pump runs on low but hums on high. Is that the capacitor?

Probably not. Two-speed spa pumps like Davey’s QB range use one run capacitor for both speeds, so a failed capacitor stops both. One speed working and the other humming points at the speed winding or the controller relay. Worth a professional look rather than a parts-cannon capacitor.

How much does a spa pump capacitor cost in NZ?

A 12µF 450V CBB60 (the most common spa-bath size) is from NZ$24.95, and the 25µF and 30µF values common on spa pool pumps are from NZ$29.95. Tracked NZ delivery. Each product page shows the delivery time for that size, so check it before you strip the pump down.

My spa pump capacitor is a metal can marked CBB65. Is that different?

CBB65 is the heavier metal-can version of the same run-capacitor technology: same job, same matching rules (match the µF on the label, same or higher voltage). We stock CBB60 in 4-80µF but not CBB65, so if yours is a metal can with mounting studs, get in touch via the contact page rather than force-fit the wrong can.

Is it OK to keep pressing the button while the pump hums?

No. A humming motor is stalled, drawing locked-rotor current several times normal, and all of it becomes heat in the windings. The thermal cut-out will trip, but every retry shortens the motor’s life. Diagnose first: a capacitor costs far less than a burnt-out pump.