Exceeding Expectations Everyday Since 1965

Part Four - Blog Series - Water Heaters: Back to Basics - Gas Valve - Lighting the Pilot

Part Four

In Part Four we will discuss Gas Water Heaters: where the flame comes from in a gas water heater, a safety device called a thermocouple, and tips on tools and maitnance of Water Heaters.

In a gas water heater, the Burner and Thermocouple are where flames heat the water in a gas water heater and safely senses the pilot light is lit, respectively.

The Burner is the source or the flame. Thermocouple (OR thermopile) is a safety device. It senses when the pilot light is on. When the pilot is not lit the gas valve will not turn the gas on.

Burner (top) Thermocouple (bottom)


Functions: Source of flame

Top Reasons for Service: Blocked airflow can cause loss of flame


Clean ‘BASE-RING FILTER’ with vacuum, if possible, so FLAME ARRESTOR can get air to feed flame

Check if closet or attic is ‘choking’ WH of air

Look for burn marks at DOOR GASKET

May need to louver door or supply attic with fresh air supply (more common is newer attics with foam insulation)


Functions: The gas water heater thermocouple

Top Reasons for Service: Build-up of emissions from natural or propane: nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), volatile organic compounds (VOCs), trace amounts of sulfur dioxide (SO2), and particulate matter (PM).

Loose Connection/Loss of Power: check connection to gas valve/replace


Clean Thermocouple with abrasive brush or cloth

Replaceable part

Manometer - test gas pressure
Do you have enough Gas Pressure?

Tool: Digital Manometer

Goal: Measuring Gas Pressures in water columns (W.C.); take measurements at the Supply (static) & Gas Valve (manifold) to assure gas-fired appliance needs are met.

Why use a Manometer: Many times a technician assumes gas pressure is “good” all the while without a numerical value from a measuring tool, you may never discover the cause of the issue.

Maintenance: Anode Rods

Functions: Sacrificial anode rods are long cylinders of aluminum or magnesium attached to a steel wire core. While it is true that all metals rust in water, different metals corrode at varying rates and that is what helps sacrificial anodes protect the steel interiors of water heater tanks.

Top Reasons for Service: Replacement every 6 month to 1 yr

NOTE: Magnesium vs. Aluminum Rods vs. KA90

Magnesium (nut has bump)

Produce a stronger current making them more effective•may react with bacteria causing a sulfurous smell

Aluminum (nut in flat)

•don’t have sulfurous smell problem as often.•

KA90 (nut green OR green dot)

•Zinc/Aluminum anode.  Zinc reduces sulfur smell.

Keeping Current with Water Heater Maintenance can add years to the life of a Water Heater

Note: Turn power OFF or set pilot light to "pilot" before performing maintenance (see Part 3 - Lighting the Pilot). Make sure water heater is completely full of water before returning to service.

1) Check Water Pressure

Check water pressure at the drain valve or hose bib. If water pressure is above maximum (80 psi), install a Pressure Reducing Valve (PRV). Water pressures are higher at night and lower during the day. If daytime water pressure is 60 psi or higher, nighttime pressures will likely be above 80 psi - install a PRV.

2) Control Water Pressures

Most experts recommend setting the PRV to 50-60 psi to protect appliances. High water pressure can damage water heaters, toilet valves, ice makers, dish washers, and washing machines. A dripping Temperature and Pressure (T&P) relief valve often means the water pressure is too high.

3) Control Thermal Expansion

Plumbing Codes have always required Thermal Expansion Tanks on close plumbing systems. Operating a water heater on a closed plumbing system without an expansion tank will damage the water heater and other appliances. Pressurize expansion tank with air before installing on a cold water line. Air pressure should match water pressure.

Always call a professional for help on water heater maintenance

4) Inspect T&P Relief Valve

Inspect the Temperature and Pressure (T&P) Relief Valve per instructions on the valve's label. T&P relief valve will drip if the water pressure is too high or due to thermal expansion on a closed plumbing system (need expansion tank). Control water pressure and install a thermal expansion tank before replacing a dripping T&P relief valve.

5) Drain and Flush Tank

Drain and flush tank (very important for gas water heaters). Turn off cold water supply, and open drain valve (connect water hose and drain to desire location, if needed). Open T&P relief valve to relieve pressure. Drain 2-3 gallons of water. If water is milky, drain entire tank. Close drain valve and open cold water supply valve. Open a hot water faucet and let hot water run for 3 minutes to make sure all air is out tank before returning to service (very important for electric water heaters).

6) Check/Replace Anode Rod

The Anode Rode helps reduce corrosion and extends life of thewater heater. Turn off power (or gas). Turn off the cold water supply and relieve pressure in the tank. Remove anode rod with 1 1/16" socket and impact wrench. Replace if significantly depleted (flexible anode rods are available if overhead clearance is tight). Check anode rods every 6 months to 3 year depending on water hardness and conditions. If a water softener is installed, check annually.


If you missed our Back to Basics Water Heater Blog Parts 1-3, the click here to read what you missed.

We have covered components, gas and electric water heaters, maintenance, tools, tips, and troubleshooting. I hope this blog series has been helpful. Contact us antime with our Live Chat customer service.

For General Water Heater Maitnace tip, vist our partners at hotwater101.com - watch this video

Visit us on Twitter @PepcoSales and Facebook/PepcoSales

Kevin Parham
June 16, 2017