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.






4 thoughts on “The Most Common Swimming Pool Heater Problems

  1. Ok, I’m at my wits end. I read everything about D.E. going back into your pool. I have taken apart the Hayward 4820 filter over and over. There is no cracks in the standpipe, the o-ring is good on it. The manifold also has no cracks in it. I checked every grid for rips . The filter is running at 10psi with a clean startup and stays running that way. My return lines do not have the D.E. blowing out when I’m filtering for hours. The pool is clean. When the filter is off that’s when it seems the DE appears . I read there can be a suction leak. I do not have air bubbles. I replaced the gasket on the lid. I also opened the multiport and the spider gasket is in good condition. So why I’m I finding light grey D.E. in my pool everyday when I wake up. I will say my motor has been acting up and is ready to go!!! Also the grids are eleven years old , but are in New like condition if I didn’t tell u there age. Is there something I’m missing here?

    1. The only other thing I can think of is filter backflush. If your system loses prime when the pump shuts off, water inside the filter tank will go two ways, through the returns or backflush through the pump and out of the suction lines. I saw this phenomenon rear its head in a pool just the other day. We depressurized the system to install a salt chlorine generator, then when we started back up we noticed a heap of DE powder by the main drain.

  2. Ok, I have a new Hayward HP50TA Heat pump. Works fantastic. Very efficient and quiet. What I can’t figure out is how to get it to turn off when the pump turns off. When 5e pump stops on its timer, if the pool is not at the set temp, the heat pump shuts the fan off and goes into FLo mode (low water flow) mode, but does not shut off. Shouldn’t the heat pump power off when the pump is not running?

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