icm22

ICM January-February 2017

Timmie McElwain Gas/Propane Basics... President, Gas Appliance Service gastc@cox.net Thermal Electricity & Electromagnetism Part 4 Learning to use these charts will ensure that a correct diagnosis of problems is done. This is particularly important as it relates to failed electromagnets. That means we need a new gas valve as we no longer can replace component parts. That can lead to a pretty expensive job and, in the case of the water heater, may mean replacing the heater versus installing a new control, depending on the age of the water heater. The procedure for using the charts is to plot the open circuit reading across the bottom of the chart and the closed circuit up the left hand side; if they intersect in the shaded area (Acceptable Range) that is an acceptable set of readings. If they intersect above the diagonal shaded area, that is an indication of a problem with the magnet assembly. This typically means a replacement of the gas valve or, depending on cost factors and customer choice, a replacement of the equipment, in particular a water heater. Any open circuit reading less than 17–18 millivolts means a replacement of the thermocouple, cleaning of the On Sept. 1, 2012 standing pilots on new equipment were done away with. This only pertains, however, to new equipment, not existing equipment. There are still many systems, both heating and hot water, that use a thermocouple as a pilot safety system. This series of articles will address these systems as to how they operate, their many uses and how to diagnose and troubleshoot thermocouple systems. These systems appear on both propane and natural gas equipment. The fact that so many are still operating makes this presentation very important. A large number of heating and water heating systems are still operating with a thermocouple pilot safety system. Being able to understand and service these systems is still vital to keeping the older systems, which still have some life in them, operating. In the next few series of articles, I am going to present some in depth information about Thermocouples and the Electromagnetic principle that works in conjunction with this very reliable and long standing system. The first chapter in my manual on Circuitry and Troubleshooting Volume II is, in fact, on thermocouples. Thermocouple and electromagnet safety troubleshooting procedures Diagnosing with charts The two charts shown in this article are used to properly diagnose, with accuracy, problems with both the thermocouple and the electromagnet. Chart 1 is to be used when there is no energy cut-off (ECO), or as some call it an automatic cut-off (ACO); these are typically found on water heaters as an extra safety feature in the water heater control to shut the system off before reaching relief valve temperature. Keep in mind that water heaters have a temperature and pressure (T&P) valve temperature and pressure, but boilers only have a relief on pressure (30 lbs). This is due to the fact that a water heater is an open system with the potential for water at 30 lbs and 250°F to flash into steam—which occupies 1,700 times as much space as water—so now the water heater becomes a rocket! The ECO is a onetime fusible link type device; what that means is if it reaches 195°F it will open and shut off the flow of millivolts to the electromagnet, causing the water heater gas flow (both pilot and main burner flame) to be shut off at 100% safe shut off. Therefore, Chart 2 is to be used to diagnose problems with water heaters and any other equipment with an additional safety, such as an ECO incorporated into the thermocouple circuit. Chart 1 Figure 1. Testing a 30 mV circuit Chart 2 22 ICM/January/February 2017


ICM January-February 2017
To see the actual publication please follow the link above