Best Practices for Troubleshooting and Repairing Gas Pool Heaters

When a pool heater stops working, homeowners, understandably, get a little cranky. They spent good money on their pool and want to be able to use it the way they envisioned—with water at a comfortable temperature. Today’s pool heaters are generally pretty reliable, but they definitely have components that occasionally need to be replaced—perhaps more so than other pool equipment. However, when a heater is not working, replacing a part, rather than the entire unit, can, and often does, solve the problem. Therefore, a service professional that is proficient in determining which part or parts need to be replaced can make the difference between a cranky customer and a happy one.

Before getting into the specifics of troubleshooting heaters, the basics should be reviewed first.

Establish and verify the symptoms

The first step when troubleshooting is to always try to get as much information from the customer as possible. Ask a lot of questions. Once arriving at the job site, observe the current state of the equipment that is having the problem. Also look at any support equipment that could contribute to the symptom. Once everything has been observed, try to operate the equipment in question to verify the fault.

Bring the necessary tools

Always have the proper tools on hand to conduct a thorough analysis of what the problem may be, e.g. a voltmeter, manometer, and a complete tool kit.

Isolate the problem

If one piece of equipment is dependent on another, such as the case with a heater and an automation system, separate them so they operate independently. There is nothing worse than trying to troubleshoot and fix a heater when the actual problem is occurring because of the automation system.

Know how it works and follow the path

Troubleshooting is simply a process of elimination. In this case, as a service professional, it is extremely important to understand how the product is supposed to operate and know the sequence or path that must be followed for it to operate properly. For example, if there is a pressure-side cleaner that is not moving very well in the pool, start where the water path begins, such as the filter pump basket or skimmer baskets, the booster pump, (if one is installed) then out to the wall fitting. Remove anything along the way that could possibly prevent the cleaner from moving, and continue this process through the water path of the cleaner. To save time, technicians often start in the area where they most commonly find problems (i.e. the wall fitting), which is acceptable, but if a problem is not found, start at the beginning. Often, the further one drills into the path, the more disassembly and detailed observation is required. The key point here is to know how something works before it can be determined what is wrong.

Verify the repair

Lastly, once the problem or defective component has been found and then repaired and/or replaced, always remember to test the repair by turning the equipment to verify its operation.

A typical troubleshooting scenario

This process should be similar for most gas pool heaters, although some of the particular details may differ depending on the manufacturer.

If the heater will not fire, start with the sources: gas and electricity. Make sure the gas supply valve is open as to avoid restricting gas flow and the heater’s gas valve is in the ‘on’ position. Also, inspect the wiring and connections to make sure the wiring harness is properly connected.

If these things check out, move onto the real troubleshooting. The first thing to inspect is gas pressure. This can be done using a manometer to measure the static gas pressure. This is the reading before the heater is fired. Next, turn the heater on, wait roughly 20 seconds and then take note of the gas pressure (after the gas valve clicks). Once the gas valve is open, the heater should run between 0.996 and 3.49 kPa (4 and 14 in. water column [WC]). A 0.498-kPa (2-in. WC) drop from static to running is normal. If the heater’s static pressure is at 1.992 kPa (8 in. WC) and drops below 0.996 kPa (4 in. WC), verify the size of the gas line and meter. A heater that starts at 203.2 mm (8 in. WC) and drops to 101.6 mm (4 in. WC), even if it is in the range, may have a supply problem. Should another gas appliance be turned on in the home, it may be enough to shut down the heater.

The heater will shut down after seven seconds if it does not ignite the gas. If the gas valve does not click open, test for 24 volts at the gas valve. If voltage is found, replace the gas valve. If no voltage is found, inspect the wiring between the gas valve and the board. If the gas valve clicks open and the smell of unburned gas is detected, the hot surface ignitor may be defective (more on this later). If the ignitor test shows it is functioning properly, verify there is nothing interfering with the ignitor (e.g. insulation). Remove the ignitor and inspect the opening. If it is clear, check all the ground connections because the hot surface ignitor senses the flame through the ground.

Be sure to check the ground connections to the ignition control module and the control board as well. On some rare occasions, the ground pins on the ignition control module or control board could be defective, interrupting the ground. Therefore, replace them if necessary.

While some troubleshooting steps are different from one manufacturer’s heater to another, there are three main components on today’s gas pool heaters that are more or less universal: the transformer, the hot surface ignitor, and the thermistor.

The transformer

Most transformers used in swimming pool heaters are step-down transformers. This means they take high voltage (usually 120 or 240 volts) and transform it to 24 volts, which is usually used by the heater’s circuit boards and its safety components. To ensure the transformer is working correctly, use a voltmeter to check the incoming voltage to the primary side (high voltage) of the transformer. Depending on the transformer, there may be two or three wires on the primary side. Place a lead on one wire and the other lead on one of the remaining wires, and then read the voltmeter for the incoming voltage. If no voltage is present, move the lead to the remaining wire. If no voltage is present, the transformer is not the problem; however, it may be in the wiring to the transformer. If voltage is present, check voltage on the secondary side of the transformer. To do this, place one lead on one wire and the other lead on the remaining wire. If voltage is not present on the secondary side, but was present on the primary side, the transformer is defective. If voltage is present, the transformer is good and other potential problems should be investigated further. Check the wiring from the transformer to the board. It could be loose or damaged. If the wiring and connectors are okay, the board is likely the problem.

The hot surface ignitor

The hot surface ignitor lights the gas mixture in the combustion chamber or box. There are different shapes and styles of ignitors, but overall, they can be tested by performing a simple resistance test. First, set the voltmeter to read ohms and disconnect the ignitor from the wire harness. Make sure the ignitor is not hot as this will affect the reading. (If the heater had just attempted to fire, give it some time to cool down). After it has cooled, place one of the voltmeter’s leads on one pin of the hot surface ignitor and the other lead on the remaining pin. It is important to know what the proper resistance is for the ignitor; most manufacturers’ specifications will include this information. If the resistance reading is anywhere outside the specified range, the ignitor is defective and should be replaced.

 The thermistor

The thermistor senses the water temperature and is also measured by a resistance reading. This reading will change depending on the actual water temperature. For example, a 10-kelvin (k) thermistor should read 10,000 ohms at 25.5 C (78 F). (Most of the leading manufacturers provide charts showing the proper resistance reading at various water temperatures.)

Using an accurate thermometer, test the water temperature. Set the meter to read ohms then, with the thermistor in place on the heater, remove the wires from the thermistor. Place one lead on each of the thermistor terminals and take the resistance reading. Refer to the manufacturer’s chart to determine if the thermistor is defective. An ohm reading outside the range specified on the chart would mean the thermistor is defective.

Sensor resistance at various temperatures

Temperature C 16 20 21 25 30 31 35 40 41
Temperature F 61 68 70 77 86 88 95 104 106
Resistance (k ohms) 14.92 12.49 11.88 10 8.06 7.69 6.53 5.33 5.1

Wrapping it up

Once it is known which part(s) require replacement, it is a good idea to report back to the pool owner, unless it was determined in advance how much they were willing to spend to repair the heater.

For instance, the conversation might go something like this: “The good news is I know why your heater wasn’t turning on. The better news is, I can fix it for (insert total cost, includinglaborr, here) and I can take care of it (right away, or name a time frame).” Do not apologize for the cost (no matter the price) or wait time (if applicable) for the repair. Always focus on the good news, which is their heater can be fixed.

This article was written by Sue Robach and originally appeared on Pool & Spa Marketing [link].