ACC Spa Pack PSOL and PSOH Errors: What They Mean and How to Fix Them

Last updated: September 2026

PSOL and PSOH errors are common on ACC spa packs, especially during first setup and testing. They’re frustrating when you’ve just finished a build and want to see the jets running, but they’re rarely a sign that anything is broken. Nine times out of ten there’s a simple fix.

In this post I’ll explain what the codes actually mean, why they appear, and how to work through the causes in a sensible order, from the free and obvious to the rare.

What do PSOL and PSOH mean?

You’ll see these codes on the topside control (the keypad you use to turn on the jets). ACC’s own error code list defines them as “Pressure Switch Open” with the circulating, low or high pump running:

Code	What it means
PSOC	Pressure switch open with the circulation pump running
PSOL	Pressure switch open with the jet pump on low speed
PSOH	Pressure switch open with the jet pump on high speed

You’ll often hear them described as “pressure switch on low” and “pressure switch on high”. That’s close enough, but the important word is open. The switch hasn’t closed because it hasn’t felt enough pressure.

What the pressure switch does

The SmarTouch Digital manual explains that the pressure switch is “sensitive to pressure inside the heater manifold”. When a pump is running, water flowing through the heater creates pressure, which closes the switch and tells the pack it’s safe to heat. If a pump is running and the switch doesn’t sense pressure, the pack assumes there’s no flow. It turns the heater off and shows the code for whichever pump should be running.

That’s a good thing. A heating element with no water moving over it overheats in seconds, and the switch is there to stop that happening. ACC packs use a pressure switch rather than the flow switch you’ll find on a lot of Balboa packs, but the idea is the same. If you’ve got a Balboa pack showing FLO instead, see Hot tub FLO error: don’t panic.

You’ll also get these codes if you power the pack up with no water in the tub. That’s normal. Fill it first.

Common causes, and how to fix them

These are rarely hardware faults. On a new tub or a new pack, the chance of the pump or the pressure switch being faulty is very slim. Work through this list in order.

1. An air lock (the most likely cause after filling)

If you’ve just filled the tub and you’re testing for the first time, the chances are you’ve got an air lock. ACC’s manual says a small volume of air gets trapped in the plumbing and the heater housing whenever a spa is drained and refilled, “lowering the pressure, disabling the pressure-switch”. It’s especially likely if you filled straight into the tub rather than through the filter housing or skimmer, whichever is at the highest point.

How to tell: turn the jets on and look for “action” in the water. Even on low speed you should see plenty of movement. You can usually hear the pump running, or put your hand near the back of the motor and feel the fan. If the pump is running but nothing is happening in the tub, you have an air lock.

How to clear it:

• Run the pump on high. ACC’s start-up instructions say to keep the high-speed pump running for at least three minutes to purge the air from the plumbing. Cycle it on and off a few times if it doesn’t clear straight away.
• Bleed it. With a pump running, loosen one of the heater fittings (or the union at the pump discharge) about a quarter of a turn until air hisses out and water appears, then tighten it again by hand. Keep a towel handy.
• Last resort: drain down and refill slowly through the filter housing or skimmer.

My full guide is Hot tub air lock: how to clear it and stop it coming back, and there’s more on filling in How to fill a hot tub with water the correct way.

2. Low water level

If the water is below the skimmer opening, the pump sucks air and the pressure at the heater drops. ACC lists a low water level as the other common cause of an air lock. Top up to the middle of the skimmer mouth and try again.

3. Gate valves closed

It sounds obvious, but it happens all the time. Both gate valves either side of the pump (and any valves on the heater loop) must be fully open before you turn the pump on. Double-check them.

4. The filter: dirty, or fitted the wrong way round

A clogged cartridge restricts flow and can trigger these codes on a tub that’s been running happily for months. Take it out, clean it and try again. The routine is in How to clean a hot tub filter cartridge.

On a new build, check the filter housing is the right way round. In-line housings have an arrow on the body, and it should point in the direction of the water flow. Fitted backwards, the housing can restrict the flow and cause flow problems. If yours is backwards, you’ll need to cut it out and turn it round.

5. Testing without the jets fitted

This one catches a lot of DIY builders. If you test the system without the jet internals screwed into the jet bodies, the water pours out of the open fittings with almost nothing to push against. That means very little back pressure in the heater manifold, so the pressure switch never closes and you get PSOL or PSOH.

Fit the jets (they just screw in), then clear the error and run the system again. There’s more on the jets themselves in DIY hot tub jets: everything you need to know.

6. A pump wired for the wrong voltage

On a US ACC SmartTouch 1000, the pack can be set up for 120V or 240V. According to ACC’s SmartTouch 1000 wiring guidelines, for 240V the pump’s blue wire has to move from the neutral terminal to Line 2 (and the blower’s red and white striped wire too). If that step is missed, a 240V pump is only getting 120V. It will hum or turn slowly, run hot very quickly and make little pressure, which gives you PSOL or PSOH.

If your pump is getting hot fast, stop, isolate the power and check the setup. My hot tub wiring guide has an ACC quick reference, including which pump cord wire is high speed and which is low. Swapped high and low wires can also cause confusing results. If the pump just hums and the shaft isn’t turning, see hot tub pump capacitors.

7. A blockage on the suction side

This is the least likely on the list, but a blocked main drain, a full skimmer basket or debris in the suction pipe starves the pump, and the pressure at the heater drops. A pump that’s starved of water often sounds like it’s full of gravel. My noisy hot tub pump guide covers that sound and how to find the blockage.

8. The pump sits above the water line

On a DIY build, a standard centrifugal jet pump has to sit below the water line, and so do the pipes to it. If it doesn’t, the pump can lose its prime and you’ll see these codes every time it starts. There’s more in Hot tub control room position and, if you’re already stuck with it, Using a priming circuit on a centrifugal hot tub pump.

9. A faulty pressure switch (rare)

Only once you’ve ruled out everything above should you suspect the switch or its wiring. ACC’s advice is clear: “Adjusting the pressure switch is best left to a trained technician.” Whatever you do, don’t bypass or jumper out the pressure switch to make the error go away. It’s the thing standing between your heater element and a dry burn-out.

Quick troubleshooting table

What you see	Most likely cause	What to do
Error straight after filling, pump running, no jet action	Air lock	Run on high for 3+ minutes, bleed at a heater fitting
Error on an established tub	Low water or a dirty filter	Top up, clean the cartridge
Error on first test, jets gushing from open fittings	No jet internals fitted	Screw the jets in
Pump hums, runs slowly or gets hot	Wrong voltage jumper, or a failed capacitor	Isolate and check the wiring and capacitor
Gravelly noise, weak flow	Suction blockage or closed valve	Check valves, baskets, drains and suction pipe
Everything checked and still erroring	Pressure switch or its wiring	Get a technician to test it. Don’t bypass it

Once the flow is sorted, the code should clear and the heater will come back on. If the tub is running but still not warming up, work through Help! My hot tub is not heating and my guide to hot tub heaters.

Common mistakes

• Filling straight into the tub instead of through the filter housing or skimmer.
• Testing the plumbing before the jet internals are in.
• Forgetting to open a gate valve after pressure testing.
• Leaving an ACC pack on its 120V wiring on a 240V supply.
• Putting the jet pump, or the pipes to it, above the water line.
• Bypassing the pressure switch “just to test it”.

Need parts, or a pack that suits your build?

The ACC SmartTouch 1000 is still my favourite pack for US DIY builds, and it’s available as a bundle with a 5.5kW flow-through heater on parts4tubs.com. Pumps, filters and other spares are at parts4tubs.com in the USA and parts4tubs.co.uk in the UK. If you’re replacing a pack rather than fixing one, see How to select a replacement spa pack.

Still planning? A lot of first-fill problems come down to where the control room sits. The Ultimate Hot Tub Control Room Guide shows how to lay out the pack, pumps and valves so they prime and bleed easily.

FAQs

What does PSOL mean on a hot tub?

On an ACC spa pack, PSOL means the pressure switch is open (not sensing pressure) while the jet pump runs on low speed. PSOH is the same on high speed, and PSOC on the circulation pump. The pack turns the heater off until it senses flow.

How do I clear a PSOL or PSOH error?

Fix the flow problem first. Usually that means bleeding an air lock by running the pump on high for a few minutes and loosening a heater fitting to let air out. Once the switch senses pressure, the error clears.

Can a dirty filter cause PSOL or PSOH?

Yes. A clogged cartridge restricts flow through the heater. Clean or replace it and check the water level at the same time.

Is the pressure switch faulty?

Rarely, especially on a new pack. Rule out air locks, valves, the filter, the water level and the pump wiring first. If it still errors, have a technician test or adjust the switch.

Can I bypass the pressure switch?

No. It protects the heater element from running dry, which can damage the heater and is a fire risk.

Got an ACC error that won’t clear? Drop it in the comments below. I read them all.

Cheers,
Andi

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Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

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