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The Most Common Swimming Pool Heater Problems

Installing and troubleshooting a heater that is still under warranty without proper licensing can forfeit your warranty under the manufacturer’s terms and conditions. If your heater is out of warranty, sometimes, it’s simply cheaper to do it yourself. If you yourself in this scenario, this blog article is for you. In this blog article, we cover the most common swimming pool heater problems a pool owner might encounter and remedies to fix the issue.

My Heater Won’t Ignite

One of the most common problems with pool heaters is it failing to ignite.

Is your heater turned ON and the temperature set correctly?

  • Ensure that the thermostat is set to a higher temperature than the current water temperature.

Is your pump running with a clean filter and basket?

  • Inspect the pump and filter and clean if necessary.

Make sure that the pilot is lit (millivolt heaters).

  • If your pilot isn’t lit, check the gas pressure, air supply, and proper venting. Make sure the pilot tube is intact and not clogged. For MV heaters, if the pilot won’t stay lit, check the output on the thermocouple.

Is the gas supply valve in the ON position?

  • Without gas, the heater won’t operate. If the supply valve is OFF, turn it ON.

Are the plumbing and filter valves open?

  • Make sure to keep your valves open as to not prevent the water flow.

Low Water Flow

In order for a heater to operate smoothly and efficiently, it’s important that pool system maintains a consistent flow of water. Manufacturers equip swimming pool heaters with pressure sensors. These special sensors monitor and detect changes in water flow. For example, in some cases, you will see a “Low Water Flow” warning pop up on your heater’s LCD screen. Or, you might notice your heater isn’t pushing out as much warm water as it should or used to. Honestly, this is a very common occurrence. If you are experiencing low water flow, or your heater won’t start, ask yourself the following questions:

Have you cleaned your filter lately?

  • Monitor your PSI reading on your filter’s pressure gauge. If the PSI is too high, clean your filter.
  • Increasing pressure goes hand in hand with the decrease of water flow.

Is your pump basket dirty?

  • Check your pump’s strainer basket. Remove the basket and remove the debris with a hose.
  • Ensure the pump basket and lid are in good conditions. No cracks.

Do you have too many water features operating at once?

  • Your pool pump only moves a certain number of GPMs, therefore, too many water features can dramatically decrease your water flow.
  • If possible, replace the motor with a larger one.
  • Close water features, or alternate them, until the pool heats to the desired temperature.

Defective Pressure Sensor/switch (Most Common)

  • The purpose of the pressure switch is to ensure that water is flowing through the unit before it allows the heater to turn on.
  • The pool pump must be ON and your filter clean for the switch to close and allow voltage to pass through.
  • Test the voltage reading on the pressure switch with a multimeter.
  • Replace the pressure switch if necessary

Are you using the low settings on your variable speed pump?

  • For operation, heaters require a minimum GPM flow. If you are running your variable speed pump on the low setting, make sure you meet the minimum GPMs for your heater.

Pool Heater Turns ON and OFF (Cycles)

If your swimming pool heater is cycling ON and OFF, it is an early indication that the electrical connection or power supply is experiencing issues. However, it isn’t ALWAYS the case. There are other factors that can actively contribute to your heater’s ON and OFF cycles.

Is your pool water chemistry consistently and accurately balanced?

  • Poor water chemistry is one of the leading causes of equipment failure, especially pool heaters.
  • Test your water before adjusting your chemical levels. If unsure, please refer to the heater’s manual for the recommended chemical levels.

Have you inspected the pressure sensor, thermal regulator, and/or the high limit switch?

  • Inspect these parts for corrosion, scaling, and/or any electrolysis issues.
  • If the pressure sensor, thermal regulator, or high limit switch is faulty, corroded, or defective- replace it.

Have you cleaned your filter?

  • A dirty filter can cause low pressure and as a result, cause the heater’s pressure switch to turn OFF. A dirty filter can prevent a heater from firing and it can also cause your heater to shut off before warming the water to the desired temperature.

When’s the last time you have inspected and cleaned the heat exchanger?

  • Deterioration of the heat exchanger can impact your heater’s operation. Inspect your heat exchanger for chemical or sanitizer damage.

Pool Heater Isn’t Heating

Sometimes, your pool heater ignites but doesn’t reach the desired temperature. Or, maybe your heater isn’t generating heat at all. Both situations are very common.

Inspect your temperature sensor.

  • Make sure you have installed the temperature sensor correctly and it is in good condition.

Double check your thermostat settings

  • Set your thermostat to a higher temperature.

Did you properly size your pool heater?

  • If your heater is undersized, it will have problems heating your pool up. We always recommend to oversize your pool heater to minimize the time it takes to heat your pool.

author avatar
Charlie Ramirez
Writer at InyoPools.com, brings a wealth of knowledge and expertise in pool care and equipment, helping pool owners make informed decisions for over a decade.

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209 responses to “The Most Common Swimming Pool Heater Problems”

  1. Craig Avatar

    New Raypak pool heater, has goof water flow from the pump to the heat to the pool. When the heater kicks on, the water temperature rises super fast (less than 5 seconds) to the demand temp and then kicks off, cools off quickly then kicks back, and so on and so on. What would cause the temperature to rise so fast like that?

    1. Matthew Simmons Avatar

      It doesn’t sound like you have enough water flow. How are you judging the strength of this water flow? Do you have a flowmeter? Are you sure you have the heater wired and plumbed in correctly?

      1. Bob D Avatar

        Matt, are you still getting these?

  2. […] main reason behind your pool heater problems or failure is water chemistry. So, examine the pH & chlorine levels to keep them at the suggested levels […]

  3. Hank Avatar

    I have a Raypak gas heater. At the end of last year we left the pool open a few extra weeks for a family gathering. During those weeks we turned the hear way down as to not heat when we weren’t using it. The pilot was lit, but the heater wouldn’t fire. (Manual not electronic) I closed the pool. Now in spring I’m trying to get it to fire, but nothing. Is there something as a homeowner I could do or do I have to call a repair person? $3000 for a heater and now annual service calls? My previous heater lasted 20 years. Raypak, 20 weeks.

    1. Matthew Simmons Avatar

      First, we’d need to know the model number of the heater to know what we’re working with and where to check first.

      1. al Avatar

        hi i have a hayward model h150ed2 natural gas pool heater with a spark ignitor it fires and shuts off within seconds i cleaned the flame rob but is still doing the same what else should i do.

        1. Matthew Simmons Avatar

          Is the heater flashing any error codes or making any off noises?

          1. Kathy M Winland Avatar

            5-F service

          2. Matthew Simmons Avatar

            From the manual: SF – Thermistor Error – An excessive temperature difference between the two thermistors (5 °F or more) or an “out of bounds” condition on both sensors (less than 10°F or greater than 180°F) will result in the error code. Automatic restart is 2 minutes after the error is corrected.

    2.  Avatar

      I agree. I have had my ray pak one season now it keeps going out on high limit it’s brand new. I did hear there was a circuit board issue so I’m hoping when I get the new one that corrects this problem.

      1. Tracy Feighery Avatar

        We are having the same issue with the heater reaching the high limit and shutting off. Heater is one year old.

        1. Matthew Simmons Avatar

          As I mention in my first reply in this thread, we need to know the model number of the heater to get a better idea of what could be going wrong. If you would like a more accurate assessment, then we need more info.

      2. Fran Avatar

        When heater ignites, sounds like it’s not getting flow or something is in it , load noises,like grinding sounds

        1. Matthew Simmons Avatar

          What is the model number of the heater? Also, are any error codes flashing when the heater fails to ignite?

          1. leonard shimko Avatar

            I have the same problem of grinding noise when running with no codes and I have a H150FDP

          2. Matthew Simmons Avatar

            I’d start by cleaning your filter either by hosing off the cartridge or backwashing; an obstruction in the gas line may also cause the grinding noise.

    3. Peter Roland Avatar

      Hi I have a h300fd Hayward pool heater
      Error code SF I checked all the wiring
      Do I need to replace the high and low temp sensors and if so do you have these parts

      1. Matthew Simmons Avatar

        SF code – Thermistor error – An excessive temperature difference between the two thermistors (5 °F or more) or an “out of bounds” condition on both sensors (less than 10°F or greater than 180°F) will result in the error code. Automatic restart is 2 minutes after the error is corrected.

  4. Rick Avatar

    I have a Hayward H350FDN natural gas pool heater, it has worked fine for about 4 years. The last time I tried to run it, won’t fire up. No error codes. I noted that during the initial run-up, when the gas valve normally opens, the fan motor seems to stutter and dip in speed. Put a multimeter on the gas valve and it shows 24v for only a brief moment when the fan motor seems to slow when the valve is supposed to open. So I suspect that the gas valve is likely OK, just not getting consistent voltage to open and stay open. Right now I suspect that the low-voltage transformer may be defective, but I’m curious if anyone else has seen these symptoms. Thanks.

    1. Matthew Simmons Avatar

      Does the display look as it should while it is starting up? After the heater fails to ignite, does the display stay on or go blank?

      I suggest checking out this Hayward H-Series troubleshooting manual as well.

  5. tom Avatar

    I have a Hayward H350 propane heater with IO code displayed. I have replace the ignitor but still have same problem and display. Was told maybe the control board was bad ?,any thoughts

    1. Matthew Simmons Avatar

      From the manual:

      IO – Igniter open error – If the control is not in lockout and senses that the igniter circuit is open when the blower is running the control will turn off the blower and go into lockout. Automatic restart 2 min after error is corrected.

      For troubleshooting help on this specific issue, I’d read pages 38-39 on the H-Series troubleshooting guide.

      1. Ed Willcox Avatar

        I have a Haywood electric heater it starts then stops. And it says low pressure switch. Where is this switch located

        1. Matthew Simmons Avatar

          What is the model number of your heater?

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