Why does my hot tub get a burning smell when the jets run on high?

[syedsam]

When I switch my hot tub jets to the high setting I get a faint burning or heated plastic smell. The water is clean and the tub runs fine otherwise. It doesn’t happen on low speed only high. Not sure if it’s the pump working too hard or something electrical. Anyone ever dealt with this?

 

[Manikshaw]

When I switch my hot tub jets to the high setting I get a faint burning or heated plastic smell. The water is clean and the tub runs fine otherwise. It doesn’t happen on low speed only high. Not sure if it’s the pump working too hard or something electrical. Anyone ever dealt with this?

Check the pump motor vents. If dust or debris blocks the airflow the pump overheats on high speed and gives off that warm smell. A quick clean usually fixes it.

 

[Zephyr]

When I switch my hot tub jets to the high setting I get a faint burning or heated plastic smell. The water is clean and the tub runs fine otherwise. It doesn’t happen on low speed only high. Not sure if it’s the pump working too hard or something electrical. Anyone ever dealt with this?

Could be the bearings starting to wear out. When they heat up under load, they give off a faint burning odor. Mine did this before the pump eventually got louder.

 

[Freddie]

When I switch my hot tub jets to the high setting I get a faint burning or heated plastic smell. The water is clean and the tub runs fine otherwise. It doesn’t happen on low speed only high. Not sure if it’s the pump working too hard or something electrical. Anyone ever dealt with this?

Also look at the wiring inside the control panel. A loose connection can heat up only when the high speed circuit kicks on. It’s a small thing that can cause big smells.

 

[syedsam]

I’ll check the vents first since the tub sits near a lot of trees. Hopefully it’s just airflow. Thanks for the help!

 

[Ella Robinson]

That burning smell when switching to high speed is usually a sign that the pump or motor is working harder than it should be, possibly due to a clog or strain. I had a similar issue, and after cleaning the filters and checking the pump for any debris, I used aquadoc jet line cleaner to clear out any hidden buildup in the plumbing. If the smell persists, it might be worth having the motor inspected by a professional.

 

[Matthew Collins]

I ran into this once and the fact that it only shows up on high speed is the big clue. Low speed doesn’t pull much current or airflow, but high speed puts everything under load. In my case the smell wasn’t the pump itself failing, it was heat buildup around it. Leaves and dust had collected around the motor shroud and vents, so once high speed kicked on, the motor got hot fast and you’d get that warm plastic or electrical smell.

Another thing worth checking is anything that only engages on high speed, like the high-speed relay or wiring terminals. A slightly loose spade connector can be totally fine on low, then heat up just enough on high to smell without tripping a breaker. I noticed mine after running high for 10 to 15 minutes, then opening the cabinet and getting hit with that smell right near the control box.

Also pay attention to how the pump sounds. If it’s louder, strained, or has a higher pitch on high speed, that can point to restricted flow making the motor work harder than it should. Filter pressure creeping up can contribute to that too. If cleaning vents and checking connections doesn’t change anything, I’d stop running it on high until you pinpoint it, smells usually show up before something actually fails. Anyone else notice theirs only smells after it’s been on high for a bit, not immediately?

 

[Liam Brooks]

I had this happen on my old Jacuzzi J-365 and it freaked me out the first time because “burning smell” and “water + electricity” is not a combo you want to ignore.

Since it only happens on high speed, that usually points to load and heat, not water chemistry. High speed draws more amps and builds more heat in the motor windings. A couple things I’d check in order:

First, flow restriction. If your filter is even partially clogged, high speed can make the pump work a lot harder. On my tub, filter pressure wasn’t crazy high, maybe 2 psi over normal, but when I pulled the cartridge and ran it briefly on high (just for testing), the smell was noticeably less. That told me the motor was straining against restricted flow.

Second, ventilation. These cabinets love to collect leaves, dust, and even insulation fibers around the motor. When high kicks on, that extra heat cooks whatever’s sitting near the housing and you get that warm plastic smell. I vacuumed out the equipment bay and made sure the motor vents were clear. Big difference.

Third, electrical connections. Like Freddie mentioned, high speed uses a different winding and relay. A slightly loose terminal can heat up only under high load. If you’re comfortable and power is fully off at the breaker, it’s worth visually checking for any darkened wires or melted insulation. If not, a tech can do that quickly.

One more subtle thing I ran into was a partially closed slice valve after service. Low speed masked it, but high speed amplified the restriction and heat. Once fully opened, the smell went away.

If the smell gets stronger over time, or you hear a change in pitch from the pump, I’d stop using high until it’s sorted. Burning odors are early warning signs, not something to let ride. Does it smell strongest right near the motor area when you open the cabinet?

 

[Megan Lawson]

I almost skipped replying since a lot of the likely causes are already mentioned, but one thing that fooled me once was the pump actually running hotter because of reduced water flow.

On my tub the smell only showed up on high speed just like you described. Low speed was totally fine. At first I thought it was electrical, but it turned out the pump was working harder than it should because of a small flow restriction. My filter looked clean after a quick rinse, but the pleats were still loaded with oils from normal use. When high speed kicked on, the motor pulled more load and heated up faster, which gave off that warm plastic smell.

What tipped me off was the sound of the pump. On high it had a slightly higher pitched tone than normal and the return flow felt weaker than it should. After I did a deeper filter clean and checked that all the slice valves were fully open, the pump ran cooler and the smell disappeared.

Another thing worth checking is the equipment bay itself. These cabinets collect leaves, dust, and sometimes insulation bits over time. When the motor runs on high and gets warmer, that stuff can give off a heated plastic or dusty smell even if the motor itself is fine.

If it only happens on high speed, it usually points to heat from load rather than water chemistry or anything in the tub. I’d check flow first, then ventilation around the pump. Does the smell get stronger if you run the jets on high for a few minutes with the cabinet open? That can sometimes help pinpoint exactly where it’s coming from.