How to Test a Geyser Thermostat with a Multimeter

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A geyser, also known as a water heater, is an apparatus used to heat water. The main principle of how a geyser works is converting electrical energy into heat energy by using heating elements. A thermostat, on the other hand, is the part that assists in controlling and maintaining the water temperature obtained when the geyser does its work. It automatically powers the geyser on and off once it reaches the set heating level.

How does a geyser work?

A geyser comprises of a water tank with two pipes fitted on the tank. One pipe act as an inlet of cold water while the other is an outlet for the hot water. The water tank contains heating elements that are regulated by thermostats. The main purpose of the thermostat is ensuring the water does not heat above the temperature value that is set. The water tank has a covering of insulating material bounded inside a metal covering. 

The heating elements in the geyser do not work at the same time, and each has its particular thermostat. The top heating component functions first until the upper tank gets hot. The function is then shifted to the bottom heating component. The thermostat primarily has two metals, each with a different coefficient of heat expansion. 

Importance of a working geyser

A geyser is one of the essential appliances you need in your home, especially if you experience cold seasons. However, if the thermostat becomes faulty, you could experience problems like insufficient heating of water. This could also lead to your water heater remaining on even after attaining the set heating level or not get power at all.

Therefore, for you to enjoy using your water heater, it is essential to regularly test your geyser thermostat and do repairs where necessary, to ensure it’s in the best working condition. The best testing device is a multimeter. 

A multimeter is an electronic device used to measure resistance, voltage, current, and other value. One of the reasons why multimeters are preferable is because you can use them for simple tests as well as sophisticated tests to detect faults in electronic items. Multimeters are of two different types, analog multimeters, and digital multimeters. 

Analog multimeters

These are meters that use analog techniques to display measurement readings. They have a graduated scale and a needle that moves over it. Analog multimeters are mainly used in detecting slow voltage changes. They have high sensitivity and low resistance, which makes them exceptional. 

Digital multimeters

Unlike analog multimeters that use a moving needle, digital multimeters are electronic meters that display readings on a screen. They are mostly preferred due to their high accuracy, high digital resistance, and the fact that they are easy to read. These multimeters are expensive than analog multimeters.

The process of testing your geyser thermostat using a digital multimeter

A geyser has two thermostats, the upper thermostat, and the lower thermostat. Before replacing your thermostat, you need to test each one of them separately to determine whether both are defective or only one. When checking your thermostat, the main thing you need to examine is the resistance of the thermostat. Here are the simple steps you need to follow to efficiently use a digital multimeter to check if the thermostat is functional.

  1. Start with disconnecting your geyser from the power supply. Unplug it if the plug is disconnectable, or turn off the power breaker if there is no plug.
  2. Remove the insulation covering of the heating elements and the thermostat.
  3. Disengage the wires from the thermostat you are to test. The thermostat uses two kinds of terminals, male-female push, and screw terminals. Use an appropriate screwdriver to loosen the screw terminals and eradicate the wires. For male-female push terminals, use the needle-nose pliers to pull the wires off. Connecting the wires to the terminals does not matter much if you are substituting them on a two-wire thermostat. Hence you can connect to any terminal. Nevertheless, if the wires are more than two, you need to label them according to the terminal number. This will enable you to rewire them to the correct terminals.
  4. Set the function switch on your digital multimeter to the ohms function. In the case where the meter is manually ranging, always set the range to the lowest. The standard lowest range on many devices is 200 Ohms. If you are using an auto-ranging multimeter, it will choose you a suitable range.
  5. Please turn on the dial on your meter and set it to R*1k, that is, resistance times 1000 ohms.
  6. Place one of your meter’s probe on the screw terminal and the other probe on the other terminal. If the thermostat is good with normally open contacts, your meter will display “OL,” indicating an open circuit. If the thermostat is not faulty and has normally closed contacts, the meter will display zero ohms.

It is essential to know that some multimeters will read the resistance of their internal fuse. That means that instead of the normal reading of zero ohms for a good thermostat, the meter reads 0.5 ohms.

Your meter reads other than zero or infinite, depending on whether the thermostat has closed or open contacts, it signifies that your thermostat is faulty. Thus, it would be best if you replaced them.

  1. Apply heat to the thermostat using an industrial hot air gun. If your thermostat has normally closed contacts, it will open, and the reading displayed on the LCD will swing from 0.0 ohms to “OL.” In the same way, a thermostat with normally open contacts will close, and the readings fluctuate from “OL” to 0.0 ohms.
  2. Reattach the wires back to the heating element. Reinstall the insulation covering on the water tanks and the plastic cover back to the thermostat. Turn on the breaker or the switch to the water heater.

The take-away

Having a water heater that is not functioning well can be frustrating for you. It is, therefore, essential for you to regularly test your geyser thermostat, which is the leading cause for defectiveness in your water heater, to ensure a well-functioning geyser. However, if your thermostats are in good condition and still the heater is not working well, then you need to check the other elements.

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