Air in the pool return lines is one of the most common solar service calls.
Some air is normal—solar systems drain every night, and the VRV (Vacuum Relief Valve) lets air in when the pump shuts off.
However, continuous bubbling indicates a system problem that must be diagnosed.
* A VRV that constantly hisses and sucks is a symptom, not the problem. Replacing the VRV will do nothing to resolve the issue.
3.1 Normal vs Abnormal Air Bubbles
✔ Normal Behavior
These are not service issues:
- A strong purge of air for 1–7 minutes immediately after solar turns ON
- Small burps of air when pump speed changes
❌ Abnormal Behavior (Service Required)
- Bubbles all day, not just at startup
- Bubbles that get worse when solar turns ON
- VRV sucking air constantly
- Air accumulates quickly inside filter tank
- Return jets spitting air even when solar is OFF
3.2 Diagnostic Method — The Filter Pressure Test (MOST IMPORTANT STEP)
This test alone eliminates 70% of bubble-related guesswork.
Step 1: Record pressure with solar OFF
Step 2: Turn solar ON
Step 3: Compare pressure
| Pressure Behavior | Diagnosis |
|---|---|
| Pressure > 25 psi (solar off) + < 4 psi rise (solar on) | Dirty filter |
| Pressure < 10 psi + NO rise when solar turns on | Skimmer/pump basket blocked OR pump speed too low |
| Pressure rises > 10 psi when solar turns on | Collectors clogged with debris |
3.3 Causes of Air Bubbles & How to Fix Them
A. Dirty Filter (MOST COMMON)
(Flowchart: high pressure off, low rise on)
Symptoms
- Bubbles only when solar is ON
- VRV sucking air constantly
- Hot collectors
Fix
✔ Instruct the customer to clean or backwash the filter
B. Blocked Skimmer or Pump Basket
Symptoms
- Very low pressure (<10 psi)
- VRV sucking air
- Pump basket cavitating
- Bubbles even when solar is OFF
Fix
✔ Clear skimmer basket
✔ Clear pump strainer
✔ Check weir door movement
C. Pump Too Weak / VS Pump Speed Too Low
Symptoms
- Bubbles only when the solar activates
- System barely primes
- Low pressure with little or no rise when solar turns on
- VRV sucking air non stop with a clean filter
- Slow or incomplete panel priming
Fix
✔ Increase RPM during solar window
✔ Lower VRV height
✔ Replace a weak filter pump with a VS pump
✔ Booster pump only if the solar system is too large for a VS pump at top speed
D. Clogged Collectors
(Usually a case of pool filter failure)
Symptoms
- Pressure spikes when solar turns on
- Hot spots on collectors (poor flow)
- VRV sucking air
- Bubbles only with solar ON
Fix
✔ Inspect for debris in manifolds
✔ Backflush system
✔ Replace old or heavily clogged collectors
✔ Advise customer to repair or replace the pool filter
E. Suction Leaks at the Equipment Pad
(Solar OFF + bubbles STILL present = suction leak)
Symptoms
- Bubbles all the time, not solar-dependent
- Pump basket never fully fills
- Air reappears in filter minutes after venting
- Water may spit from fittings only when pump is turned off
Common Leak Sources
- Pump lid O-ring dry or cracked
- Loose pump lid
- Loose/warped suction valve
- Cracked union
- Water level at or below skimmer mouth
- Blocked skimmer weir
Fix
✔ Lubricate or replace O-ring
✔ Tighten unions
✔ Replace cracked lids or suction valves
✔ Raise water level
✔ Clear weir blockage
3.4 Air Bubble Problems That Are NOT Solar Problems
These issues get blamed on solar because solar adds lift and exposes marginal conditions—but they originate elsewhere.
A. Low Skimmer Water Level
✔ Raise water level
✔ Ensure weir door moves properly
B. Pump Lid Leak
✔ Replace lid or O-ring
✔ Lubricate and reinstall
C. Suction Valve Leaks
✔ Replace diverter and O-rings
✔ Replace valve if cracked
D. Variable-Speed Pump Programming Errors
✔ Increase RPM during solar operation
✔ Disable aggressive low-speed schedules
3.5 Installation-Related Bubble Issues
These normally appear shortly after installation:
A. Weak filter pump
✔ Lower VRV
✔ Increase VS pump speed in solar mode
✔ Replace an old, weak pump
B. Reversed Feed and Return Lines
Rare, but sometimes happens when there is an underground pipe run
Listen to riser pipes when the solar is first activated. If the supply pipe slushes loudly, the pipes are reversed and the system is flowing backwards.
Symptoms:
- Constant bubbling
- Air gurgle in feed line
- Hot spots on collectors
- Noisy supply pipe
Fix:
✔ Swap lines at equipment or roof
C. Long or High Elevation Runs
✔ Increase pump RPM
3.6 Complete Field Testing Procedure
All techs should follow this exact order:
- Filter pressure test (off vs on)
- Check skimmer & pump baskets
- Check pump lid O-ring & suction valves
- Observe VRV behavior
- Feel collector surface for hot spots
- Run flow-direction “swish test”
- Check for reversed plumbing
- Check RPM settings
- Inspect manifolds for debris
3.7 Key Takeaways
✔ Air bubbles are a symptom, not a cause
✔ Replacing the VRV is never the solution
✔ Most bubble calls relate to filters, pump RPM, or suction leaks
✔ Reversed solar plumbing is a possibility on newer installations
✔ Bubbles with solar OFF = suction problem
✔ Bubbles only with solar ON = flow problem
✔ The pressure test solves most diagnostics in under 60 seconds
