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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. Tim R. Avatar

    Hello Matt,
    I have a Jandy LXI 400 natural gas heater and recently I started spa and heater and all seemed to be good, but after waiting almost 45 minutes the spa never started to heat up and the heater appeared to be running fine with no faults.

    1. Matthew Simmons Avatar

      Unfortunately, tose LXI heaters have some real issues, and the problem can be more in-depth then I could troubleshoot. I suggest contacting Zodiac (Jandy) to see if they can walk you through a troubleshoot or can have a tech come out.

  2. Adrienne F. Avatar

    Hi,
    Thank you in advance for any insight you may have on this. Our pool/spa heater wasn’t heating the spa much. Temperature would rise a little, but it wasn’t getting the water hot. Water from the jets didn’t feel much warmer than the spa water. The heater seemed to be getting hot. Our home warranty replaced the heater today (Hayward 400FDP) after 2 hours the water went from 56 to 78. Water from the jets still doesn’t seem any warmer than the spa water. Outside temperature mid 60’s. It used to heat to 100 in about a half hour. There is plenty of propane.

    1. Matthew Simmons Avatar

      If it was just installed and you are having issues, you should get the company back out there to take a look at the heater. You may want to check that only the spa is being heated, not a combination of the pool and spa. There could be an issue with the gas line not being big enough which is an issue if you upped the size of the heater from the old one. The latter should definitely be checked by a professional.

  3. Sam Avatar

    I have a Raypak 280 swim pool heater and the temp is set 32 Deg. I can see the the pilot light and the gas being lit but it goes off just after few seconds. The pump pressure is good, i can see the water travelling into the heater through the clear check valve. the gas tap is on at all times. have anyone came across this fault ever.

    1. Matthew Simmons Avatar

      This is symptomatic of low gas pressure or low water flow. If propane, check the level of fuel in the tank. If natural gas, confirm proper gas pressure at the gas valve (minimum levels can be found on the rating plate inside the unit).
      Is there a fault indicated on the control panel?
      If water flow is insufficient (less than 1.6 lps), then it could be tripping one of the overtemp sensors. Confirm proper water flow through the heat exchanger. Clean and/or backwash the filter. Empty all baskets. If not, it could be scale or blockage inside the exchanger.

  4. Arlene Avatar

    Hello I have a Rheem 8350 pool heater. The pool heater states it’s 104 and keeps shutting off but the actual temperature is 84 what could be wrong.

    1. Matthew Simmons Avatar

      It could be a bad temp sensor. But, that model uses two sensors with different Ohm ranges. There is a way to check that the PC board is reading the right range.
      The best thing to do is to call the heat pump service line 800-375-7378, and they can walk you through the process. You will need to be at the unit and will need serial number and date of installation handy.

  5. Matthew Avatar

    MiniMaxNT LNSeries. Pool pump on – it fires up fine within 15 seconds or so. Pool features off and pool return is on full. I have the heater set to 102 and it is starting at 60. It only heats up to about 62 after an hour. The water coming out of the spa return is just warm, not hot.

    1. Matthew Simmons Avatar

      This is our guide for Pentair MiniMax NT Heater Error Codes. Is your heater lashing an error code? If so, that would be important info to know. This is the Owner’s Manual for the Pentair Minimax NT LN Series.

      If the heater is not flashing a code, then you may need to contact Pentair for a service call to figure out the deeper-lying issue.

  6. Jonathan Avatar

    I have a Hayward h400idl and i first had a fire on the board, so i replaced it, then it wasn’t getting gas so i replaced the gas valve. Then i was getting the ao code, so i replaced the blower. It worked for one night on the hot tub, and then i got the ao code again. I sent it back, got a new one and new hoses and the blower vacuum switch and the vent pressure switch. I got ao code quick and i noticed the blower was really hot. The hoses looked like they moght be melting. Any ideas? TIA

    1. Jonathan Avatar

      I guess you have no idea.

      1. Matthew Simmons Avatar

        Sorry, your question got skipped, fell behind because of vacation. In the interim, I would have suggested contacting the manufacturer for their expertise.

        As for the blower being hot, that is pretty standard because it is sitting over the heat exchanger and next to the exhaust stack. You may want to make sure you have the circular insulation mat that sits between the blower’s flange and the stack. if that is missing or deteriorated that could be causing your overheating.

        h400idl blower assembly

      2. kevin browning dallas tx Avatar

        did you ever find out the problem with excessive heat blower barbs?

  7. Adin Lane Avatar

    Hi Matt
    I have a raypak PCO 430 gas heater. Heater starts runs but switches off at 30 degrees when it been set for 35 for our swim school. Heater was off for two weeks in our holiday period,
    Any help with solving this issue would be greatly appreciated. You are a knowledgeable guy.
    Cheers and thanks again
    Adin

    1. Matthew Simmons Avatar

      When the heater is shutting off, is it giving a service code on the display? Could be shutting off due to low water flow to the heater “O”. Or if F2, F3, or F4 is coming up then it is a sensor problem. Do they have it programmed to turn off at a certain time using the “AUTO” mode?

      1. Justin Avatar

        I’m having exactly the same problem. I can’t get the unit out of Auto mode. I just want to manually set the temp and the pool warm up to that temperature.

        1. Matthew Simmons Avatar

          As you can see, I was asked them about error codes to which they did not answer. So I’ll try with you. Were there any error codes?

  8. Mike H Avatar

    I have a Pentair Master temp 200 heater. The temp reading started fluctuating quickly from 81 to 85. The setpoint is 84. The heater burner kicks on and off following the temp fluctuations. I replaced the thermistor and cleaned the control board and connections. Same results. Is this a control board issue?

    1. Matthew Simmons Avatar

      Follow these troubleshooting instructions for the MasterTemp on page 38, hopefully, you can verify if the board is good through those steps.

  9. Frankinbarrie Avatar

    What does Option valve light on mean on a Hayward pro logic control panel mean?

    1. Matthew Simmons Avatar

      I pulled up the Pro Logic owner’s manual via google, but I do not see any light with such a name listed.

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