Hot tub startup after draining (and how to fix an air lock)

To start a hot tub after draining: close the drain, install a clean filter, fill through the filter compartment to above the highest jets, turn the breaker on, run each pump briefly to push air out, then balance the water and let it heat with the cover on. If a pump hums and no water moves, you have an air lock. Fix it by pulsing the pump between speeds or by slightly loosening the pump union with the power off until water appears.

Startup, step by step

1. Power off. Confirm the breaker is off before you start filling.
2. Check the equipment bay. Drain valve closed and capped. Pump drain plugs in. Unions hand-tight. Slice (gate) valves fully open.
3. Open every jet. Closed jets trap air.
4. Install a clean or new filter. On tubs where the hose fits beside it, some owners fill with the filter out and install it once the tub is full. Either works.
5. Fill through the filter compartment. This pushes water into the plumbing first and forces air out through the jets. Use a hose pre-filter if you have hard or well water.
6. Fill to the right level. Above the highest jets and about halfway up the skimmer opening. Stop there.
7. Turn on the breaker. The tub enters priming mode for 4 to 5 minutes on many systems. Balboa panels show Pr or a purge-air message.
8. Prime each pump. Press the jets button to run the pump on low, then high, for 10 to 15 seconds each. You should see strong flow from the jets. Repeat for each pump.
9. Check for leaks. Look in the equipment bay with a flashlight for drips at unions and plugs.
10. Balance the water. See the order below.
11. Cover and heat. Latch the cover. Heating takes hours.

How to fix an air lock

An air lock is a bubble trapped in a pump's wet end. The impeller spins in air and cannot move water. Do not let a pump run dry for more than about 15 seconds at a time. It will damage the shaft seal.

Method 1: pulse the pump

1. Make sure the water level is correct and all jets are open.
2. Turn the pump on low for 10 to 15 seconds, then high for 10 to 15 seconds, then off.
3. Repeat three or four times. Each surge moves the bubble. Many air locks clear this way, and you will hear the pump note drop when water arrives.

Method 2: bleed at the pump

1. Turn the power off at the breaker.
2. Open the equipment bay and find the affected pump. Put a towel under it.
3. Some pumps have a small bleeder screw on top of the wet end. If yours does, open it slowly by hand until air hisses out and water follows, then close it.
4. If there is no bleeder, loosen the large union nut on the pump's discharge side (the pipe leaving the top or side of the wet end) a quarter to half a turn. Air will hiss out.
5. When water starts to dribble steadily, tighten the union by hand. Do not use a wrench with force. The o-ring does the sealing.
6. Dry the area, restore power, and run the pump.

This is plumbing work only, done with the power off. Do not open the control box. If the unions are hard to reach, corroded, or will not reseal, call a technician.

Method 3: push water backward

With the power off and the filter removed, hold a garden hose against the filter compartment's suction opening for a minute or two. The hose pressure pushes water through the pump and drives the air out.

Startup chemistry, in order

Step	Target	Notes
1. Metal or scale control	Per label	Only for well water or hard water. Add first.
2. Total alkalinity	80–120 ppm	Always before pH
3. pH	7.2–7.8	Recheck after alkalinity settles
4. Calcium hardness	150–250 ppm	Raise if fill water is soft
5. Sanitizer	Chlorine 1–3 ppm or bromine 3–5 ppm	Bromine tubs: build the bromide reserve per label
6. Shock	Per label	Cover off for at least 20 minutes

Add one product at a time with the jets running, wait 20 to 30 minutes between each, and follow the label for your tub's volume. Never mix products. Retest once the water is above 80°F, since cold water reads and reacts differently. Full targets are in the ideal levels chart.

Messages you may see during startup

• Dashes (--): the temperature is not known yet. Normal for the first couple of minutes.
• dr, dry, HTR MAY BE DRY: air in the heater. Bleed the air lock and reset. See HTR MAY BE DRY.
• FLO or flow messages: air or a filter problem. See FLO.
• COOL or a cold-water message: normal on a fresh fill. It clears as the tub heats.

If it is not heating after a few hours

Check that the temperature has risen at all. On 240V expect 3 to 6°F per hour, on 120V 1 to 2°F per hour, and a 120V heater usually pauses while the jets run on high. If the reading has not moved, see hot tub not heating.