When it comes to looking at the common causes of pool heater failure, many are linked to improper installation. Therefore, pool professionals who wish to ensure pool water heats up and stays warm when needed should take the time to review the heater installation for each pool they maintain. Here are some of the critical parameters.


  • Make sure the pool water is balanced at all times.
  • Make sure heater is venting properly.
  • Inspect burners and heat exchanger periodically for any sign of chemical damage or soot build-up.
  • Always make sure heater area is clear of debris, especially the area where the heater is venting.
  • Always ensure there is proper water flow going through heater.


Proper heater sizing

It is vital for any residential or commercial pool heater, along with other components of the equipment pad/room, to be correctly sized for the pool and any additional bodies of water that may be connected. (Hot tubs, splash pads, etc.) To properly size the equipment, heater specifications should be consulted and compared to the flow rate that will be pumped through the unit.

To calculate an approximate heater size for a pool, technicians must do the following:

A Determine the desired pool water temperature.

B Determine the average temperature for the coldest month the pool will be used (if it is an outdoor pool).

C Subtract the average temperature for the coldest month from the desired pool water temperature. This will provide the temperature rise needed.

D Calculate the pool surface area in square feet.

E To determine the required Btu output for gas pool heaters, multiply the pool area (in square feet) by the temperature rise (ideal water temperature/ average temperature in coldest month) by 12.

To clarify, heaters are sized based on a 24-hour temperature rise. Therefore, a heater with 1 million Btus takes 24 hours to raise the pool temperature 15 degrees for a 5,450 square foot pool. Based on this information, the appropriate heater can be selected for the pool.

If the heater does not appear to be sized properly, it should be replaced. In fact, replacing older heaters with new, energy-efficient units not only provide improved water heating but will also reduce energy consumption and lower operating costs in the process.

Gas meter sizing

Just as it is important for the heater to be sized properly, it is also important that the gas meter is sized appropriately for the heater. Assuming the pool heater uses natural gas, the meter must be sized — at minimum — to the capacity of the heater itself. In other words, if one is using a 400,000 Btu heater, the meter should be capable of providing 400,000 Btus. Always remember that there may be other items pulling gas from that same meter, which must be taken into consideration when properly sizing a gas meter. Low gas pressure can cause damage to the internal components of a heater, causing build-up that leads to blockage of the heat exchanger.

Propane tank

If the pool heater is fueled by propane, the tank must be large enough to supply the proper amount of gas to the heater. Improper gas pressures to the heater (while in operation) will cause heater inefficiencies and possibly a build-up of soot, which could damage the burners as well as the heat exchanger.

Gas line and venting

Once again, sizing is very important. The gas line to the heater, as well as the venting of the heater, need to be sized and vented properly. When venting heaters, it is important to maintain proper clearances 6 inches from combustible surfaces on the top and side of the unit. Check the heater manufacturer's manual for recommended clearances.

When considering requirements with respect to how far a heater can be vented, or how far ductwork can run to pull intake air, each 90-degree elbow reduces the maximum horizontal polyvinyl chloride air intake run by 12 feet. Each 45-degree elbow reduces the maximum run by 6 feet.

At a minimum, the room in which a heater is installed must be equipped with two permanent air supply openings: one within 12 inches of the ceiling and the other within 12 inches of the floor for combustion air. This installation procedure is in accordance with the American National Standards Institute Z223.1, National Fuel Gas Code, as applicable, and any local codes that may apply.

RELATED: How to Size a Pool Heater

Air supply openings should directly, or through a duct, connect to outdoor air. In the past, venting and air intake ducts had to be in balance and be the same length; however, newer heaters draw combustible air from outside the structure and force out flue gases.

The color of the heater's flame is a good indicator of whether or not the unit is receiving enough combustible air to function properly. A clear, blue flame indicates the unit is burning 100 percent of the gas. If the flame is not getting enough air, it becomes orange and releases carbon that turns to soot and clogs heat exchangers.

One of the more common mistakes that occurs when installing a new heater is upgrading the size of the unit without having a large enough gas supply. For example, if the pool previously had a gas line for a 200,000 Btu heater and the new unit is rated 400,000 Btus, the gas line also needs to be bigger to accommodate the increased output.


The symptoms associated with heater failure can generally be narrowed down to issues with a burner or heat exchanger. The following are a few troubleshooting tips to consider for common problems experienced with pool heaters.

Loud, high-pitched whine

This symptom is generally associated with a burner issue — specifically, with the flame being too "rich." To remedy this, check the pressure tap between the gas valve in the blower inlet and verify the gas regulator setting is -0.2 in. water column. In some cases, it might be necessary to replace the gas orifice.

Flame is "fluttery"

Again, this is symptomatic of a burner issue and can be accompanied by an acrid smell from the exhaust. However, in this case, the cause is most likely the result of the flame being too "lean" — the burner may even fail to remain lit. As noted earlier, check the pressure tap between the gas valve in the blower inlet and verify the gas regulator setting is -0.2 in. wc.

Flame does not stay lit

Sometimes the combustion on the heater appears to be normal but the flame does not stay lit. The cause is most likely a result of the flame not being detected. To remedy this situation, check the igniter to see if it is wet or possibly damaged. The igniter may need to be replaced.

Further, verify the burner flame holder is properly grounded. This might also require the ignition control module to be replaced. Finally, be sure to inspect the manifold pressure. In doing so, check the gas supply line pressure when the heater is operating.

Boiling and "bumping" sounds

The heat exchanger can also be the cause of several problems. One of the most common issues is the boiling of water accompanied by "bumping" sounds. This is commonly caused by low water flow to the heater. It can also be caused by a plugged heat exchanger or a bypass valve that is stuck open.

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The best way to fix this problem is to ensure the pump and filter are working properly so the water flow is sufficient to the heater. If the heater is not getting good flow, check to make sure your filter is clean — if not, it may be time for backwash or element cleaning.

Reduced water flow

If water flow is too fast, you'll see condensation. If it is too slow, the heater is not warming the water efficiently. In some cases, a pump that is not working properly can contribute to heater inefficiencies due to irregular water flow. If this is the problem, it might be a good time to consider a variable-frequency drive to ensure the water flow through the heater remains consistent.

The heat exchanger could also be plugged because of improper water chemistry, resulting in scale formation. More often than not, this is because the water is out of chemical balance. If this is the case, the water should be tested to ensure the proper corrective measures are taken to get the water back in balance.


Propane and natural gas, when burned, produce water as a byproduct. If the heat exchanger is too "cool," the humid flue gases will condense on the fins of the heater. Condensation on the heat exchanger causes carbon to adhere to it. The condensate collects, then drops on to the burners. The combustion is then compromised as the condensate interferes with the flame pattern.

This poor combustion turns into soot, which collects on the fins and impedes the flue gasses. The condensation not only causes inefficiencies in heater functionality, but also causes oxidation on copper from low return water temperatures.

Brief periods of condensation on start-up is normal for most pool heaters. In fact, all category I and III pool water heaters will condense if allowed to send very low return water into the heat exchanger. However, adding airborne chemicals to condensate on heat exchanger coils will cause the unit to fail more quickly. As mentioned earlier, "sooting" is often the first sign of a problem, but is often ignored. In fact, some service technicians who have not been trained properly may place jumpers on safety devices instead of paying attention to the sooting that occurs.

Soot formation on heat exchanger tubes

There are several items to look for to identify soot formation on heat exchanger tubes. The first contributor to the problem is low gas pressure. The heater needs an 11 in. wc for propane gas and a 4 in. wc for natural gas. The pressure of the gas should be inspected while the burners are lit.

Soot can also form when there is too much water flow through the heater. To remedy this, install a high-flow modulator or a manual bypass valve. Obstruction of the burners by some foreign matter can also be a problem; therefore, it is important to remove, inspect and clean all burners.


All service technicians should establish a comprehensive maintenance program for the equipment pad/room, which must include a specific action plan for heaters, as well as the pumps and filtration systems used on pools and other water features.

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It is also a good idea to keep additional parts on hand just in case an aquatic facility needs to get a heater up and running immediately. Having access to items such as pilot assemblies, orifice parts for burners, and even a gas valve can come in handy during a time of need. It can also be wise to post your company's phone number directly on the heater for emergencies. Avoiding heater problems in cool seasons is important to all service technicians and, often times, the simplest best practices are the ones that keep pools running smoothly at all times.