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Water Heating Plumbing Terminology 101

February 23, 2024
Water Heating Plumbing Terminology 101

Plumbing may seem intimidating at first. After all, plumbers have trained to work with complex systems that keep your home running. Here at Rheem®, we leave plumbing to the professionals, but we encourage homeowners to be familiar with plumbing terminology. This guide makes understanding and communicating with your plumber easier.

We recommend looking at our water heating mini-glossary first to learn the basics of water heaters and water heating measurements.

A Guide to Plumbing Terms

Reviewing the different water heater components can help you communicate with your plumber and understand how a water heater works. Here are some plumbing terms you can use to diagnose issues or simply impress your plumber.

New and aging anode rodAnode rod – The sacrificial metal rod (usually magnesium or aluminum) in the water heater that attracts corrosive material like minerals and sediment and protects the inside of the tank. Have a plumber inspect your anode rod every year to extend your water heater’s life.

Pictured: an anode rod before and after corrosion. The anode rod on the left has life left before it needs replacing.

Flushing – A routine maintenance that involves turning off your water heater and flushing out sediment buildup. Please call your local plumber once or twice a year to perform this important step in maintaining your water heater.

Gasket – A closed, sealed refrigeration system that makes heating water extremely efficient. If worn or broken, water will leak from the gasket.

Heating elementsHeating element – The device that heats water in electric water heaters. Our Rheem ProTerra® Hybrid Electric Heat Pump Water Heater also has heating elements as a backup for the heat pump.

Pictured: a copper heating element on the left (good material) and a stainless steel heating element on the right (better material).

Heat exchanger – A device that transfers heat from the burner to water. It’s the main component in tankless gas water heaters, which heats the water on-demand.

Heat pump – An extremely efficient technology consisting of a compressor, condenser, evaporator, closed refrigerant system and fan that pulls in heat energy from the air to heat water. The Rheem ProTerra Hybrid Electric Heat Pump Water Heater and the Rheem ProTerra Plug-in Heat Pump Water Heater models use this innovative technology to produce zero carbon emissions and deliver energy savings.

Mixing valve – A mechanical or electrical device that mixes cold and hot water to deliver tempered water. A mixing valve placed on the outlet water connection ensures water leaving the tank is a safe set temperature even if the water in the tank is super-heated above 120°F.

Combustion chamber – The part of the gas water heater where air and fuel are mixed to create combustion. Gas water heaters manufactured after 2003 have sealed combustion chambers where the gas pilot is lit using an ignitor mechanism.

Pilot assembly – Consists of a pilot, ignitor and thermocouple that connects the burner and the gas valve. Pilot is a small flame that ignites fuel from the open gas valve traveling to the burner.

Thermocouple – A sensor used to detect the presence of a pilot flame. It’s a crucial safety device that prevents the release of flammable gas if the pilot light is out. This is the part usually replaced, not the burner.

Water heater rating plateRating plate – A label on the water heater that lists information about the unit: model number, serial number, manufacturer, warranty length, when it was manufactured and other essential information. Locate it on the water heater so that you’re prepared to take a picture or provide information for your plumber.

Shut-off valve – An accessory part of the water heater that helps protect your home from water damage. When liquid is detected by the leak sensor rope, the valve shuts off the inlet water supply to the water heater limiting leaks. The Rheem ProTerra Hybrid Electric Heat Pump Water Heater with built-in LeakGuard has an auto shut-off valve.

Temperature and pressure valveT&P (temperature & pressure relief) valve – A safety feature designed to protect water heaters from overheating and over-pressurization. If the tank pressure or temperature exceeds normal limits, the valve opens releasing water through a pipe preventing tank unsafe conditions.

Thermostat – A mechanical switch on non-smart water heaters that turns the heating element or burner on or off. The switch opens turning the elements or burner off when water reaches desired temp and closes when the water temperature cools. There can be two thermostats: an upper and lower thermostat, each sensing the water temperature at the top and bottom of the tank.

Thermistor – A resistor on smart water heaters assists the control board in regulating the water temperature. It produces electrical resistance (measured in ohms) based on air or water temperature. The control board reads the ohms and determines water heater response.

Homeowner Education

There is a lot more that goes into plumbing than this terminology, but knowing plumbing and water heating references is a good start. When there is a problem, using the above terminology will help a plumber diagnose and service your water heater.

Make Sure You Schedule Annual Maintenance

Annual professional maintenance is recommended for your water heater to maintain a comfortable home. Find a professional Rheem plumber or contractor near you:


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