Checking for fuel supply issues
If the heater runs through its cycle but will not ignite, it is likely there is a more complicated fuel supply issue.
The number one issue many technicians find in the field with malfunctioning pool heaters is the use of undersized gas piping. Most installation and operation manuals provide gas piping sizes based on the capacity of the unit and the distance from the heater to the fuel source, whether it is an LP tank or a natural gas meter.
Gas systems are designed on pressure and distance. It is worth noting, by distance it means developed pipe length. This represents the length of the pipe including the pressure drop created by elbows and other fittings. A technician can determine whether the size and length of the gas piping is adequate by reading the installation and operation manual.
Further, it is critical to verify the gas valve inside the unit is functioning properly; therefore, technicians should check to ensure there is voltage going to the valve. If voltage is detected, it means all other safety devices in the unit are functioning as intended.
At this point, a monometer must be used to verify there is incoming gas pressure to the valve. Some valves allow a technician to check the manifold pressure to verify there is sufficient pressure on the burner side of the valve. All these values are unit-specific and will be outlined clearly in the manual.
In the event the gas valve opens and there is sufficient pressure, yet the heater still fails to ignite, sputters, or runs for a brief period before shutting down, the control is not seeing establishment of flame (flame proving). This could either be the result of a defective flame sensor or an insufficient gas supply. Simply verifying there is sufficient gas pressure at the burner at one moment in time is not enough for a technician to say with certainty that gas supply is not the issue.
The ladder chart in the manual will show both static and dynamic gas pressure must be verified. Checking static gas pressure must be completed while all other appliances on the same gas supply are running at the same time, but with the pool heating unit off. Checking dynamic gas is the same as static, except the pool heating appliance will be turned on.
If the dynamic gas pressure drops below manufacturer requirements at any point, this suggests the issue is an undersized piping system, regulator, or meter. Just because most heaters have a 19-mm (0.75-in.) gas pipe connection does not mean 19 mm is sufficient of the developed length of pipe.
Technicians should always ask the client about any changes on the property that could cause the problem at hand. Even small additions to the load on a gas meter can be the culprit, such as installing a larger gas range, or adding a gas fireplace or outdoor fire pit
Like in the 1983 movie, A Christmas Story, just because one has an electrical outlet, it does not mean they can simply continue to plug in more lights. The same applies for gas meters.
In fact, many times, gas supply issues can only be fixed by increasing the pipe size or pressure. To do either, a licensed gas professional is required to replace the necessary components.
Evaluating the power supply
Electrical issues are often the result of work done on the property, such as the addition of outdoor lighting. Any changes or additions can create a variable; therefore, a technician should try to eliminate these variables before diving into a deeper diagnosis.
If power is delivered to the heater properly, and the unit is not functioning as intended, most heaters have some form of built-in diagnosis displayed on the control interface. The display may report there is a sensor error, or where the error stems from. However, technicians must keep in mind, a sensor error does not mean with certainty the sensor is bad. In many cases, the sensor is doing its job exactly as it is designed for the safety of the system.
This is another reason it is critical to have the installation and operation manual, which will show the probable causes of a specific sensor error. A technician should work through the manual and use process of elimination to determine the source of the sensor error.
Testing system water flow
Flow is one of the simpler issues to diagnose. As previously mentioned, the heating unit will be equipped with a pressure or a flow switch to ensure flow is established. If flow is not present, the unit will not fire.
The most frequent cause of a low- or no-flow situation is clogged filters. The second most common issue is an inoperable or underperforming pump.
If these issues are presenting, technicians should clean the filter, check the pump, and consult the heater manual to determine what the correct flow rate through the heat exchanger is. This should be checked against a flow meter on the effluent side of the heat exchanger. If there is insufficient flow, the piping system may not be designed or installed correctly, or the pump is undersized. One way to avoid this is by installing variable-frequency drive (VFD) powered booster pumps on all pool heating systems, so the filter and heater loops are hydraulically separated.
Much like diagnosing any mechanical problem, fixing pool heating systems is best done via process of elimination. It takes time, it takes the right tools, and it takes the appliance manual. An experienced technician also helps expedite the process.
Author
Tom Soukup is the principal of Patriot Pool Heating Co., with over 20 years as a hydronic designer and installer. He specializes in high-efficiency and green technology and brings his expertise to custom commercial work, pool heating, and agricultural projects. Soukup can be reached at twsoukup@patriotpoolheating.com
