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Electric Pool Heater Troubleshooting: Fixing Common Problems

Electric pool heater not working? This guide covers everything from simple resets to complex electrical issues you can diagnose yourself.

Table of Contents

Why Isn’t My Electric Pool Heater Working?

Electric pool heaters are actually pretty simple compared to gas heaters.

They use heating elements (like giant versions of whats in your electric water heater) to warm the pool water.

The most common call we get: “My electric heater stopped working.” Nine times out of ten, its either a tripped breaker or a bad heating element. Simple stuff.
Basic Components: Electric heaters have heating elements, a thermostat, a flow switch, contactors (relays), and safety switches. When any of these fail, the heater stops working.
Symptom Most Likely Cause Quick Check
Completely dead, no lights No power (breaker off) Check breaker panel
Breaker trips when heater starts Bad heating element or short Test elements with multimeter
Heater on but not heating Failed heating element Check if elements are getting power
Heating but very slowly One or more elements failed Test each element separately

First Steps in Any Diagnosis:

Step 1: Check the breaker – is it on?

Step 2: Look at the heater display – any error codes?

Step 3: Is water flowing through the heater?

Step 4: Feel the pipes – are they getting warm at all?

No Power to Heater

If your heater display is dark and nothing happens when you turn it on, theres no power getting to the unit.

Common Power Issues:

  • Circuit breaker tripped or off
  • GFCI tripped (common in pool equipment)
  • Loose wire at disconnect box
  • Failed transformer (provides low voltage for controls)
  • Blown fuse on control board
  • Bad disconnect switch

Power Troubleshooting:

Step 1: Go to breaker panel, find heater breakers (usually 2-pole, 40-60 amp)

Step 2: If tripped, reset and see if it holds

Step 3: Check disconnect box near heater – should be “on”

Step 4: Look for GFCI breakers and test/reset them

Step 5: Check for loose wires in junction boxes

⚠️ Danger: Electric pool heaters run on 240V which can kill you. Always turn off the breaker before opening any electrical panels or boxes.

According to Pentair’s electric heater documentation, proper electrical connections are critical for safe operation.

Breaker Keeps Tripping

If your breaker trips every time the heater tries to start, somethings drawing too much current.

This is usually a bad heating element or a short circuit somewhere.

Why Breakers Trip:

  • Heating element shorted to ground
  • Water got inside electrical components
  • Breaker itself is worn out
  • Loose connection creating arcing
  • Too many things on same circuit (rare for pool heaters)
Important Test: If the breaker trips immediately when you turn it on (before heater even starts), theres a dead short. Call an electrician.

Isolating the Problem:

Step 1: Turn off heater power at disconnect

Step 2: Reset breaker – does it stay on now?

Step 3: If yes, problem is in the heater

Step 4: If no, problem is in the wiring between breaker and heater

Step 5: Test heating elements with multimeter (see section below)

Had a customer who kept resetting the breaker for weeks. Finally called us. One heating element had failed and was shorting out. It melted part of the wiring inside the heater. A $150 element repair turned into a $800 electrical repair because they waited.

Heating Element Failures

Heating elements are the most common failure point in electric pool heaters.

They burn out over time, especially if you have hard water or chemistry problems.

What Kills Heating Elements:

  • Scale buildup from hard water
  • Corrosion from unbalanced chemistry
  • Running dry (no water flow)
  • Age – they dont last forever (5-10 year lifespan)
  • Power surges

Testing Heating Elements:

Tools Needed: Multimeter set to resistance (ohms)

Step 1: Turn off ALL power to heater

Step 2: Disconnect wires from element terminals

Step 3: Test resistance between the two terminals

Good Element: Shows 10-30 ohms (check your model specs)

Bad Element: Shows infinite resistance (open circuit) or zero (shorted)

Multiple Elements: Most electric heaters have 2-6 heating elements. If one fails, the heater still works but heats slower. Test them all.
Element Test Result What It Means Action
10-30 ohms Element is good Test next element
Infinite (OL) Element is burned out Replace element
Zero or very low Element is shorted Replace immediately
Fluctuating reading Element failing or bad connection Replace soon

For element replacement procedures, check Hayward’s service documentation.

Flow Switch Problems

The flow switch is a safety device that prevents the heater from running without water flow.

If it fails or gets stuck, the heater wont turn on even when water is flowing fine.

Flow Switch Symptoms:

  • Heater wont turn on despite good water flow
  • Flow error code on display
  • Heater works intermittently
  • You can hear switch clicking but heater doesnt start

Testing the Flow Switch:

Step 1: Make sure pump is running and water is flowing

Step 2: Locate flow switch (usually on side of heater)

Step 3: With power off, test with multimeter for continuity

Step 4: Should show continuity when water flows, open when no flow

Step 5: Clean or replace if not operating correctly

Common Fix: Flow switches can get gunked up with debris or scale. Sometimes just removing and cleaning it solves the problem.
⚠️ Never Bypass: Some people bypass the flow switch to “fix” the problem. This is dangerous and can destroy your heating elements if water stops flowing.

High Limit Switch Issues

The high limit switch shuts down the heater if water temperature gets too hot.

When it trips, the heater stops heating until the switch is manually reset.

Why High Limits Trip:

  • Low water flow causing overheating
  • Thermostat set too high
  • Failed flow switch letting heater run dry
  • Scale buildup on elements trapping heat
  • Faulty high limit switch tripping prematurely

Resetting High Limit:

Step 1: Turn off power to heater

Step 2: Locate reset button (usually red, on top or side)

Step 3: Press firmly until you hear/feel a click

Step 4: Turn power back on and test

Step 5: If it trips again immediately, you have a bigger problem

Repeated Trips: If your high limit keeps tripping, dont just keep resetting it. Figure out WHY its overheating. Usually its a flow problem.
Customer kept resetting their high limit switch daily. Turns out their filter was completely clogged, water flow was terrible, and they were slowly cooking their heating elements. By the time we got there, two elements were toast.

Thermostat Malfunctions

The thermostat controls when the heater turns on and off based on the water temperature you set.

When it fails, you get either no heating or constant heating.

Thermostat Problems:

  • Display shows wrong temperature
  • Heater wont respond to temperature changes
  • Buttons dont work or are unresponsive
  • Display is blank or garbled
  • Heater runs constantly regardless of temperature

Thermostat Troubleshooting:

Step 1: Try resetting – turn off breaker for 5 minutes

Step 2: Check actual pool temp with separate thermometer

Step 3: Set thermostat way higher than current temp

Step 4: Listen for contractors clicking when it should start

Step 5: Check for loose wires at thermostat connections

Digital vs Mechanical: Older heaters have mechanical thermostats (dial type). These can often be cleaned and adjusted. Digital ones usually need replacement if they fail.

Most modern electric heaters use digital controls. Check Jandy’s control system documentation for troubleshooting specific models.

Contactor Problems

Contactors are basically heavy-duty relays that switch power to the heating elements.

When you hear a loud click as the heater starts up, thats the contactors engaging.

Signs of Bad Contactors:

  • No clicking sound when heater should start
  • Clicking sound but heater doesnt heat
  • Buzzing or humming from contactor
  • Contacts look burned or pitted
  • Contactor feels hot to touch

Testing Contactors:

Step 1: Turn off all power

Step 2: Remove contactor cover (if accessible)

Step 3: Look at contact points – should be clean and smooth

Step 4: Test coil with multimeter (should show resistance)

Step 5: Replace if contacts are badly pitted or coil is open

Replacement Cost: Contactors are relatively cheap ($20-50 each) and not too hard to replace if your comfortable with electrical work.
⚠️ Hot Contractors: If a contactor gets very hot during operation, its failing and needs immediate replacement before it causes a fire.

Temperature Sensor Faults

The temperature sensor tells the thermostat what the water temperature actually is.

If it gives wrong readings, your heater might think the water is already warm when its not.

Sensor Issues:

  • Display temp doesn’t match actual pool temp
  • Heater shuts off prematurely
  • Heater runs longer than needed
  • Erratic temperature readings
  • Sensor error code on display

Testing Temperature Sensor:

Step 1: Compare display reading to actual pool temp

Step 2: If more than 3-5°F off, sensor might be bad

Step 3: Check sensor for corrosion or damage

Step 4: Test sensor resistance with multimeter (consult manual for values)

Step 5: Replace if readings are way off spec

Sensor Types: Most electric heaters use thermistor sensors. Resistance changes with temperature. Typical values are 10K ohms at 77°F, but check your model.

Heater Runs But Heats Slowly

If your heater is running but takes forever to heat the pool, one or more heating elements probably failed.

The heater keeps working with the remaining elements, just at reduced capacity.

Causes of Slow Heating:

  • One or more heating elements burned out
  • Scale buildup reducing heat transfer
  • Low voltage to heater
  • Heater undersized for pool volume
  • Heat loss exceeding heat gain

Diagnosing Slow Heating:

Step 1: Note how long it takes to raise temp 1 degree

Step 2: Test all heating elements with multimeter

Step 3: Check if all contactors are engaging (clicking)

Step 4: Verify voltage at heater matches nameplate requirements

Step 5: Inspect elements for scale buildup

Performance Math: A typical 57KW electric heater should raise a 20,000 gallon pool about 1-2 degrees per hour. If its way slower, somethings wrong.
Heater Rating Pool Size Expected Heating Rate
11 KW 5,000-10,000 gal 2-3°F per hour
25 KW 10,000-15,000 gal 1.5-2.5°F per hour
57 KW 15,000-25,000 gal 1-2°F per hour
120 KW 25,000-40,000 gal 1.5-3°F per hour

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