Why is My Pool Heater Not Working Efficiently? 7 Common Reasons and Fixes

Check for scale buildup, clean the filter, and inspect the heater’s components for blockages or malfunctions.

1. Dirty or Clogged Filter

A dirty pool filter restricts water flow, which can prevent your heater from working properly. When flow is reduced, the heater either struggles to operate or shuts off to protect itself. The result? Cool water that takes forever to warm up.

What to look for:

• Water jets feel weaker than usual

• Heater frequently shuts off

• Pressure gauge shows higher-than-normal readings

What to do:

• Check the pressure gauge on your filter. High pressure usually means it's clogged.

• Clean or replace the filter cartridge if necessary.

• Rinse cartridge filters thoroughly with a hose

• Backwash sand or DE filters according to the manufacturer’s guidelines

Neglecting the filter is one of the most common mistakes pool owners make. It doesn’t just affect the heater, either. Poor filtration can also lead to algae growth and cloudy water.

2. Low Water Flow Rate

Pool heaters are built with flow sensors. If there's not enough water moving through the heater, it won’t fire up or will shut off mid-cycle.

Common reasons for low flow:

1. Clogged skimmer or pump baskets

2. Air leaks on the suction side of the pump

3. Incorrectly sized pump or plumbing

4. Valves set incorrectly

5. Worn-out pump impeller

Fix it by:

• Turning off the system and checking for debris in baskets

• Looking for visible bubbles in the pump strainer (a sign of air leaks)

• Checking valve positions to ensure proper flow path

• Consulting with a pool technician to confirm pump size matches your system

Even small obstructions or air leaks can disrupt flow enough to confuse your heater into shutting off.

3. Faulty Thermostat or Incorrect Settings

Thermostats act as the brain of your heater. If it’s misreading water temperature or set incorrectly, your water may never reach your desired warmth.

Signs of a thermostat issue:

• Heater turns off before reaching set temperature

• Digital display shows inaccurate readings

• No response when changing settings

Steps to take:

• Make sure the thermostat is set higher than the current water temp

• Calibrate or replace the thermostat if readings seem inaccurate

• For mechanical dials, make sure they turn smoothly and don't stick

Some newer models allow remote or app-based control. In these cases, check your app settings to ensure they match your preferences.

4. Gas or Electrical Supply Issues

Whether your heater runs on gas or electricity, it needs a steady energy supply. Interruptions or fluctuations can cause weak heating or total shutdown.

For gas heaters:

• Ensure the gas valve is fully open

• Listen for ignition clicks or check pilot lights (for older units)

• Inspect the burner for dirt or rust that might prevent ignition

For electric heaters:

• Inspect your breaker panel for any tripped breakers

• Confirm the unit is getting power with a voltage tester or multimeter

• Look for corroded or loose wiring inside the control box

If you're not familiar with electrical or gas components, this is a good time to involve a licensed professional. Working with power sources can be dangerous if done improperly.

5. Heat Exchanger Problems

The heat exchanger is where your pool water gets its warmth. If this component is blocked or corroded, efficiency drops fast.

Common heat exchanger issues:

• Scale buildup from hard water

• Rust or corrosion, especially in saltwater systems

• Internal blockages from debris or chemical residues

Maintenance tips:

• Use a descaling solution every season if you have hard water

• Flush the exchanger with fresh water after heavy use

• Consider a cupro-nickel exchanger for saltwater pools, which resists corrosion better

When neglected, a clogged heat exchanger doesn’t just cause inefficiency. It can overheat the heater, leading to expensive repairs or total unit failure.

6. External Temperature and Pool Cover Use

You might be surprised by how much heat your pool loses to the environment. Wind, cool air, and even nighttime temperatures can undo your heater’s work.

Without a pool cover:

• Pools can lose up to 5 degrees Fahrenheit overnight

• Heat loss is faster on windy or cloudy days

• More energy is needed to maintain your target temperature

Simple ways to reduce heat loss:

• Always use a pool cover at night

• Invest in a solar cover to passively raise daytime water temperature

• Use windbreaks like fences or hedges to shield your pool

Even the best heater will struggle if your pool loses heat faster than it gains it.

7. Age of the Heater

Every machine has its limits. Pool heaters typically last 8 to 12 years. Older units tend to struggle more, even if they still technically work.

Signs your heater might be too old:

• Slow heating time

• Frequent error codes or shutdowns

• Rising energy bills despite regular use

If your heater is getting up there in years:

• Check the model's expected lifespan in the owner’s manual

• Weigh repair costs against the cost of replacement

• Look into newer models with better energy efficiency ratings

Modern heaters often feature digital controls, better sensors, and more durable parts. While a new unit costs more upfront, it may pay off in lower utility bills and fewer breakdowns.

Regular Maintenance Makes All the Difference

Keeping your heater running efficiently isn’t about fixing big issues all the time. Most of the time, it’s about routine care.

Build a simple maintenance schedule:

• Weekly: Clean skimmer and pump baskets

• Monthly: Inspect filter, pump, and thermostat

• Seasonally: Flush the heat exchanger, check wiring, and inspect valves

• Annually: Schedule a professional tune-up

It’s a lot easier to catch a small issue before it becomes a big one. Regular attention keeps performance high and prevents costly emergency calls.

When to Call a Pro

You don’t have to go it alone. There are moments when calling a certified pool technician is not only smart, but necessary.

Call a professional if you notice:

• Strong gas smells

• Electrical burning odors

• Rust, smoke, or water pooling around your heater

• Constant error codes you can’t resolve

Many pool techs offer seasonal service packages that include heater checks, so you can avoid surprise issues when you really want to use your pool.

Fixing a pool heater isn’t always about complex repairs. Often, it comes down to understanding the basics and keeping up with regular care. When you know what to look for and how to respond, your pool stays comfortable, your costs stay low, and your heater lasts longer.