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You need to drain your hot tub for cleaning. Should you turn off the power? Will a hot tub even run without water?
A hot tub will run without any water if the power is turned on. There are some protections, but this could be damaging to the hot tub’s internal components and should be avoided by turning off the power to the hot tub before draining the hot tub completely.
If this is something that happened to you, read on to find out what steps you need to take.
What Parts Of A Hot Tub Require Water To Work Properly?
Ok, so now we know that a hot tub can run when it is completely empty. This may seem counterintuitive because surely the hot tub manufacture would have done something to guard against it, right?
The short answer is it depends heavily on the model of hot tub you own. Most hot tubs will have a water flow or pressure sensor that measures the water flowing through the hot tub heater. The sensor is usually placed close to the heater. If the pressure or flow is measuring low, the hot tub controller can take action to disable components that could be damaged.
Let’s consider the major internal components of a hot tub:
- On board sanitizers (UV, Ozone, Salt System)
A hot tub heater works similarly to the hot water heater in your home. It converts energy into heat and transfers that heat to the water. A hot tub heater is designed to heat moving water.
The pumps in a hot tub create the water pressure and flow needed for the jets to operate. There are many different kinds of pumps, but in a hot tub, the most common is a centrifugal pump. An electric motor drives an impeller that has blades that pull water from the inlet and push it out of the pump.
There are a couple of different types of onboard sanitizers that could be installed on your hot tub.
- UV Sanitizers – Use UV light to kill living organics in the water
- Ozonators – Produce Ozone which kills living organics and oxidizes other contaminates in the water
- Salt Water Systems – Produce chlorine from salt through a process called electrolysis to sanitize the hot tub water
What Happens To the Heater Without Water?
Hopefully, nothing will happen if the hot tub only runs for a short period of time without water. If the water stops moving or runs dry, the heater can quickly overheat itself and all the components around it. This could cause a wide range of damage depending on the exposure time.
Think about what happens when you turn a stove burner on without a pan or pot. The coils will glow bright red and get a lot hotter than they normally would. That is exactly what happens to your hot tub heater. The heater element is designed to heat given a specific heat transfer rate by conduction and convection into the flowing water.
Without water, the heat will not flow effectively out of the heating element causing it to overheat. Without flow, the water remaining in the heating tube will boil eventually turning to steam which could over pressurize the plumbing lines. Not a good thing to happen.
In the best case scenario, the hot tub will have a flow sensor that will disable the heater if low flow is detected. This is an important safety measure as a heater running with improper flow could damage the spa plumbing, injure hot tub users, and if run long enough become a massive fire risk.
What Can Go Wrong If A Pump Runs Dry?
Like the hot tub heater, the pumps are designed to always run with water. The pumps create flow by turning an impeller. When the hot tub is full, the water in the plumbing provides resistance against the spinning impeller. When there is no water, there is no resistance. With less resistance, the pump motor will spin faster and faster until the impeller resistive force once again equals the force the motor is able to produce.
Overspeed can cause damage in a couple of ways:
- The impeller could crack from the increased velocity.
- The electric motor could overheat.
- The pump seals could crack due to increased speed and therefore friction.
- The pump bearings could be damaged or have their life reduced.
Are Any Other Components Subject To Damage?
If the hot tub is equipped with a UV Sanitizer, the blub used to create the UV rays will produce heat. In some cases, this could be a lot of heat. Normally that heat would mostly be transferred to the flowing water. If the hot tub is empty, that heat has no efficient path to travel. In a UV sanitizer, the bulb is surrounded by a quartz tube that amplifies the UV radiation. Quartz is naturally resistant to heat, but everything has a breaking point. If run too long, the bulb or quartz tube could be damaged.
The final component that could be damaged is the hot tub plumbing. Damage to the plumbing would be a side effect of another component meltdown. This would most commonly occur near the heater where excess heat could melt the plastic plumbing lines. Another area of concern would be around the pumps. Excess heat or physical damage caused by overspeed could expand to melt or crack surrounding plumbing.
How Do You Turn Off A Hot Tub?
Hot tubs, if powered by electricity, are run at two voltage levels: 110/120V and 220/240V. If your hot tub is powered by a 110/120V source, then you simply need to unplug it from the electrical outlet like you would any other appliance in your house. These hot tubs have a standard GFCI electrical cord and might also be referred to as a “Plug & Play” hot tub. Once you unplug the hot tub, it will be safe to drain and work on.
If your hot tub is powered by a 220/240 source, then you will need to find the GFCI breaker that the hot tub is connected to. The breaker will either have a switch like most home electrical panels, or some other mechanism that can be removed to break the electrical circuit. Like the “plug & play” hot tub, once the power is removed, it is safe to drain the hot tub.
Both types of hot tubs can be turned back on by reversing the above steps. Remember to only do this once the tub is fully filled to the minimum level defined in the owner’s manual (usually just above the highest jet).
What Steps Should You Take If This Happens To You?
If you ever find yourself in a situation where your hot tub kicks on while empty, don’t panic. Follow these simple steps and you will hopefully not cause any damage.
Step 1: Remove power from the hot tub
As soon as you realize the hot tub is running, remove power immediately following one of the methods described above. The sooner the power is removed, the better. The longer the components are exposed to this scenario the higher the risk of damage.
Step 2: Inspect the hot tub for damage
Once the power is removed, you will want to check the hot tub for any obvious signs of damage. Obvious signs might include;
- Abnormal odors or smoke
- Any visible physical damage such as cracked or melted pipes, damage to the heater assembly or pump assembly
- Water leaks
You may have to remove the hot tub skirt to perform this inspection.
Step 3: Complete the original planned activity
You were draining the tub for a reason so go ahead and finish that activity. There is not much else you can do with the tub empty to troubleshoot so complete your task and move on to the next step.
Step 4: Refill the hot tub
When it is time to refill the hot tub, make sure you remove the filter and fill the hot tub through the filter intake. This will limit the risk of air being trapped in the plumbing. Since the hot tub ran dry there is likely a lot of air in the plumbing lines.
Tip: You should fill your hot tub this way every time.
Step 5: Turn back on the power
Once the hot tub is filled to the minimum fill line. Turn the power back on to the hot tub.
Step 6: Inspect the pumps for leaks
With the pumps running, visually inspect the exterior of the pump housing looking for any signs of water. Check the seals around the motor shaft for any signs of water leakage.
Step 7: Breath and relax
If you were able to complete all the above steps without any issues, then you should be good to go. Be happy that nothing happened and remember to turn your hot tub off next time!