If you own a swimming pool with a connected hot tub — also called a spillover spa — and you’ve ever noticed that the hot tub drains when the pool pump turns off, you’re not alone. This is one of the most common problems reported by pool owners with spa-integrated systems. One day, your spa is perfectly full and bubbling. The next morning, the water has dropped several inches, or even down to the jets — and the pool water may look a little higher than usual.
So what’s going on here?
In most cases, your spa is not structurally leaking — it’s draining into the pool through the plumbing system when the pump turns off. This can be caused by a failed check valve, a leaky Jandy valve, air leaks, automation problems, or plumbing issues in the return or suction lines. The good news is that it’s almost always fixable — and often without major repairs if caught early.
In this article, we’ll take a deep dive into:
How pool/spa combo systems work
Why water flows from your spa into the pool when the system shuts off
The most common causes of spa water loss
DIY and professional troubleshooting steps
When it’s time to call in a leak detection expert
Let’s begin by understanding how your system is intended to function.
How Pool and Spa Combo Systems Are Designed to Function
Most modern inground spas are connected to the pool’s plumbing system. These are commonly referred to as pool/spa combo setups or spillover spas because the spa gently overflows into the pool when operating in pool mode.
Here’s how a typical system works:
Shared Plumbing: The pool and spa share a pump, filter, and heater.
Jandy Valves: These 3-way valves direct suction (where the water originates) and return (where water is discharged).
Check Valve: A one-way valve on the spa return line keeps water from flowing backward.
Elevated Spa Design: The spa is raised higher than the pool, and water flows from the spa into the pool during regular operation.
During pool mode, water is pulled from the pool drains and skimmers and returned to both the pool and spa. The spa overflows into the pool, keeping it circulated and clean. In spa mode, water is pulled from the spa drains and directed solely to the spa jets, creating a therapeutic bubbling effect.
When the pool pump shuts off, the system is designed to maintain a closed circuit, allowing water to remain in place until the system is turned back on. But if anything is leaking, misconfigured, or broken — especially the check valve — gravity will cause water from the higher spa to drain down into the lower pool.
Gravity: The Main Force Behind Your Spa Draining
The root cause of most spa drainage issues is simple: gravity. Water always seeks the lowest level. Your spa sits higher than the pool, so unless a valve is actively holding the water back, it will naturally flow downhill into the pool when the pump is off.
Think of a spillover spa as a small bowl sitting above a large one. When the water is being pumped uphill, it stays full. When the pump shuts off, and nothing stops it, the water will start running back down the pipes and refill the lower bowl — your pool.
Your plumbing system is supposed to prevent that from happening. When it doesn’t, the spa drains — sometimes a few inches, sometimes more. The amount it drains and how quickly it can help diagnose what exactly has gone wrong.
The Most Common Reasons a Spa Drains When the Pool Pump Turns Off
Let’s examine the top five causes of spa drain issues in detail.
1. Failed Check Valve (Most Common Cause)
The check valve is a one-way valve installed on the spa return line. It allows water to be pumped into the spa but blocks it from flowing backward when the pump is off.
If this valve is:
Worn out
Stuck open
Missing entirely
Clogged with debris
Installed incorrectly
…it can no longer prevent the water from flowing back down into the pool. The result? The spa slowly (or sometimes quickly) drains down until it matches the pool’s water level.
What to check:
Look for a clear-lidded valve labeled “Check Valve” on your return lines.
Open it (with the pump off) and inspect the flapper or spring mechanism.
Replace if the internal seal is warped, missing, or stuck.
This is one of the most common service calls we receive — and fortunately, replacing a check valve is a relatively easy and inexpensive repair.
Note: When removing your spa’s check valve for examination, ensure that your spa’s water level is not above the level of your pool equipment. If it is, and you open your spa check valve, you will have a massive flood on your hands very quickly.
2. Faulty Jandy Valves
Your Jandy valves (suction and return) control where water is pulled from and sent to. If the internal seals are leaking, they may allow water to pass through even when the valve is “closed” to that circuit.
Examples:
If the return valve is leaking, spa water can be pulled into the pool return lines.
If the suction valve is leaking, spa water can siphon backward into the pool suction lines.
In either case, your spa loses water after the pump shuts off.
What to look for:
Valve handles do not fully turn to the “Spa” or “Pool” position.
Worn rubber seals inside the valve body.
Valve actuators (automatic motors) stuck mid-rotation or improperly programmed.
3. Automation or Timer Malfunctions
In automated systems, valve actuators are controlled by the pool’s control system or timer. If these actuators fail or are misadjusted, they may leave the spa and pool valves partially open, allowing water to escape.
This creates a path for the spa to drain into the pool even if the check valve is working correctly.
Symptoms:
Spa drains inconsistently or only after the scheduled program runs.
Valve actuators often stop short or make noise but fail to rotate correctly.
Manually turning valves stops the problem temporarily.
Fixes may include:
Recalibrating actuator stop points.
Replacing a faulty actuator.
Reprogramming automation settings to ensure proper valve closure during pump shutdown.
4. Air Leaks on the Suction Side
When air enters the system — primarily through a suction-side leak (before the pump) — it can disrupt the natural vacuum and allow water to drain backward.
Common air leak locations:
Pump lid O-ring
Valve stems
Loose unions
Cracked fittings
Suction lines with minor cracks
Signs:
Air bubbles in the spa when the pump is running
“Gurgling” sound when the system shuts off
Spa drains slowly over hours rather than immediately
While a check valve might still be functioning, the presence of air allows water to bypass it more easily — similar to letting go of a finger on a straw.
5. Leak in the Spa Return or Suction Lines
If your spa continues to drain below the pool level, that’s a big red flag. It usually means water isn’t flowing back into the pool — it’s leaking out of the plumbing system entirely.
Common causes:
Cracked underground return lines
Leaking suction lines near the spa drain
Loose jet fittings
Seepage through the spa light conduit
How to tell the difference:
If the spa drains only to the pool water level, check the valve or valve for failure.
If the spa drains below the pool, it indicates a structural or plumbing leak.
In these cases, professional leak detection is essential.
DIY Troubleshooting: Steps You Can Take
If you want to attempt a diagnosis yourself, here’s a step-by-step approach:
Step 1: Watch the Drain Pattern
Does it drop fast or slowly?
Does it stop at pool level or go lower?
Fast drop = wide-open path (valve or check failure)
Slow drop = minor leak or air entry
Drains below pool = plumbing leak
Step 2: Check the Pool Water Level
If the spa drains and the pool level rises, it’s not a leak — it’s a backflow issue.
Step 3: Inspect the Check Valve
Open the lid
Check the flapper or spring
Replace if needed
Step 4: Manually Turn the Diverter Valves
Turn the suction and return valves to isolate the spa fully. Turn off the pump and watch the spa.
If water holds = the problem is with the valve alignment
If it still drains = check valve or leak
Step 5: Test for Air Leaks
Inspect the pump lid and O-ring
Run water over joints and fittings — if air bubbles stop, that’s your leak
Listen for gurgling at the shutdown
Step 6: Run in Spa Mode
If the spa still drains when isolated in spa mode, that suggests the leak is in the spa plumbing or structure itself.
When to Call a Professional Leak Detection Company
If you’ve tried the steps above and your spa still drains, it’s time to bring in the experts.
Professional leak detection companies can:
Pressure test your return and suction lines
Inspect check valves and diverters
Use dye testing and sonar listening tools to find hidden leaks
Confirm if the issue is structural or plumbing-related
This is not a guesswork job — pressure testing with specialized plugs, listening devices, and even scuba inspections may be necessary. The cost of waiting too long can be high, especially if the pump begins to run dry or water loss increases.
Fix the Issue and Keep Your Spa Full
A spa that drains every time your pool shuts off can be annoying — but it’s usually very fixable. Whether it’s a worn-out check valve, a leaky valve seal, or something deeper in the plumbing, identifying the issue early can save you water, energy, and costly damage to your equipment.
At Precision Leak Detection, we specialize in identifying and solving pool and spa plumbing issues like this. From pressure testing your spa lines to replacing faulty valves and finding hidden leaks, our team has the experience and tools to get your system running like new.
Whether you live in West Palm Beach, Boca Raton, Boynton Beach, Delray Beach, Wellington, Jupiter, Palm Beach Gardens, Lake Worth, or any surrounding area — we service all of Palm Beach County and are ready to help.
If your spa drains when your pool turns off, give us a call today. We’ll inspect, diagnose, and solve the problem quickly and professionally so you can enjoy your pool and spa the way they were meant to be used.
Contact Precision Leak Detection — Palm Beach County’s trusted leak detection experts.
