Filter Pressure Too High

Why Your Filter Pressure Spikes and What to Do About It

Your pool’s filter pressure tells you how easily water is moving through the system.

When pressure is too high, it means water is being restricted, which can damage equipment, reduce flow, and cause heaters or salt systems to shut down.

This guide covers the most common causes of high filter pressure and what you can check before requesting service.

⭐ 1. Dirty or Clogged Filter (Most Common Cause)

A dirty filter creates resistance, causing pressure to rise.

Signs:

✔ Pressure gauge reading higher than normal

✔ Weak return jet flow

✔ Low Flow light on salt system

✔ Heater shutting off

Fix:

• Clean cartridge thoroughly
• Backwash sand/DE filters
• Replace cartridge if old or collapsed
• Ensure pressure drops after cleaning

If pressure rises again quickly, the pool likely needs a shock or deep cleaning.

⭐ 2. Algae or Cloudy Water Loading the Filter

Even if the water looks okay, microscopic algae can clog a filter extremely fast.

Signs:

✔ Pressure rises again within hours

✔ Filter becomes dirty immediately

✔ Water slightly cloudy or dull

✔ Low chlorine levels

Fix:

• Shock the pool
• Run pump continuously 24–48 hours
• Clean filter multiple times during treatment

This is one of the most common reasons filters clog quickly.

⭐ 3. Air Not Venting from the Filter

Trapped air increases pressure inside the tank.

Check:

✔ Air relief valve open and working

✔ Filter tank lid O-ring sealed

✔ Pump is fully primed (no air draw)

Fix:

• Open air relief valve until steady water flows
• Fix suction-side air leaks
• Lubricate filter O-ring

⭐ 4. Return Valve Partially Closed

Any restriction on the return line increases pressure.

Look for:

✔ Return valve not fully open

✔ Spa return slightly engaged

✔ Solar valve partly closed

✔ Bypass valves misaligned

Fix:

• Ensure all return valves are fully open unless intentionally bypassing

⭐ 5. Salt Cell or Check Valve Blockage

Debris or scale in the salt cell creates extra resistance.

Signs:

✔ Pressure increases after heater

✔ Visible scale in salt cell

✔ “Low Flow” or “Check System” warnings

Fix:

• Clean salt cell
• Check for debris
• Inspect check valve flapper for sticking

⭐ 6. Heater Internal Bypass Issue

If your heater’s internal bypass sticks or fails, pressure may spike.

Signs:

✔ Pressure rises only when heater is on

✔ Heater cycles or shuts off

✔ Loud water rushing inside heater

This requires professional inspection.

⭐ 7. Multiport or Diverter Valve Issue (Sand/DE Filters)

A worn spider gasket or stuck diverter valve increases internal resistance.

Fix:

• Inspect multiport gasket
• Ensure valve fully seats in FILTER position
• Replace gasket or valve if worn

⭐ 8. Pump Running Too Fast (VS Pumps)

High RPM creates high pressure, especially with:

• Small filters
• Long plumbing runs
• Restrictions in return lines

Fix:

• Lower pump RPM
• Use high speed only when necessary (spa, heat, cleaning)

⭐ 9. Piping or Fittings Partially Blocked

Rare, but possible due to:

✔ Debris buildup

✔ Collapsed pipe

✔ Broken check valve internals

✔ Construction debris in line

Requires professional diagnosis.

⭐ 10. Filter Media Issues

For sand or DE filters:

✔ Old sand becomes compacted (“channeling”)

✔ DE grids damaged

✔ Manifold cracked

These conditions drastically affect pressure.

Fix:

Filter teardown or media replacement.

⭐ When to Contact Professional Pool Company

Call us if:

✔ Pressure stays high after cleaning filter

✔ Pressure spikes again within a day

✔ Heater shuts off due to flow

✔ Return jets extremely weak

✔ Filter leaks or makes unusual noise

✔ Air constantly builds inside tank

✔ You suspect a blocked or collapsed pipe

We can diagnose:

• Internal filter damage
• Heater bypass failures
• Plumbing restrictions
• Impeller issues
• Salt cell blockage
• Air leaks or trapped air

⭐ Summary

High filter pressure is usually caused by:

• Dirty or clogged filter
• Algae or cloudy water
• Trapped air
• Valve misalignment
• Salt cell scale
• Heater bypass failure
• Multiport valve issues
• High pump RPM

Most causes can be solved with proper cleaning and correct valve setup.

⭐ Need Help?

If your filter pressure remains high after cleaning, contact Professional Pool Company. We can identify plumbing or equipment restrictions and restore proper flow.

Updated on: 29/11/2025