Hi, I'm Vance and welcome to Repair and Replace.
Your water heater works hard to give you a steady supply of hot water.
In this episode we'll learn how gas water heaters work and then
we'll look at some of the differences between standing pilot and power vent models.
Lets begin.
A standard water heater burns gas to heat the water stored inside the insulated tank.
When hot water is used, cold water enters through a dip tube and fills the bottom of the tank.
The gas control valve uses a built in thermostat to monitor the water temperature.
When the thermostat senses the cold water, it opens up the main gas valve.
Air is drawn from below the tank and mixes with the gas.
The main burner ignites, and the exhaust fumes rise up through the flue vent.
The burner continues to heat the water until the set temperature is reached.
The temperature and pressure relief valve
is by far the most important safety device in water heaters.
If the pressure or temperature inside the tank gets to high, the relief valve
will open and release water, preventing the tank from exploding.
Additionally every water heater has a drain valve at the bottom
which can be used to flush the tank of sediment.
If too much sediment builds up it will act as an insulator reducing the efficiency.
This is why its best to flush the tank once a year during regular maintenance.
Regardless of the type, all water heaters need protection against corrosion and rust.
The tank is coated with a thin glass lining but it doesn't always cover 100% of the tank.
Also the glass can become cracked, exposing more of the tank walls.
On the top of the tank sits the anode rod.
Like a lighting rod the anode attracts the corrosive elements in the water, sacrificing
itself to protect the tank.
If the anode dissolves completely, or if the rod is completly incased in calcium,
then the corrosive elements will start attacking the exposed metal.
Most anode rods will last 4 - 6 years, but this depends on the pH and purity of the water.
This is why its best to check the anode rod during regular maintenance.
All water heaters have a relief valve, drain valve and an anode rod,
but ignition and venting is different in Standing Pilot, and power vent models
Older homes will generally have a standing pilot water heater, with an atmospheric vent.
They use a small pilot flame that burns continuously,
igniting the main burner when heat is needed.
This is the standard design that has been used for decades
and is easily identified by the metal exhaust pipe.
Since its the pressure from combustion that pushes the exhaust upwards,
these heaters must be vented vertically.
Any restriction in the airflow might cause backdrafting,
which can extinguish the pilot flame.
These tanks are generally replaced with newer standing pilot models,
since connecting to the existing vents keeps replacement costs low.
Standing pilot water heaters will either use a conventional or an electronic gas valve.
Conventional gas valves are powered by a thermocouple.
The thermocouple sits in the pilot flame,
and generates a small amount of electricity when heated.
About 20 - 30 millivolts.
This produces enough electricity to power the gas valve.
The thermocouple also acts as a safety switch.
If the pilot light goes out, then the thermocouple will cool down, the voltage will drop and
the gas valve will shut off.
This prevents unburnt gas from being released into your home.
Electronic valves require more power as they have additional circuitry and diagnostics.
These valves are powered by a thermopile, which is a pile of thermocouples bundled together.
When heated by the pilot flame thermopiles generate around 600 - 750 millivolts.
Electronic valves will also flash an error code when something goes wrong.
And these are often listed on the valve.
Now if the pilot isn't staying lit, then it's most likely a problem
with the thermocouple or thermopile.
Alternatively it could be an issue with the thermal cutoff switch.
The thermal switch protects against overheating.
If the temperature in the combustion chamber gets too high,
the thermal switch will shut off the gas valve.
The thermocouple, thermopile and thermal switch can all be tested.
You can learn more in the troubleshooting videos linked in the description.
Unlike standing pilot heaters, power vent models don't rely on atmospheric pressure.
Instead they use a draft inducer blower to push the exhaust through the vent.
This makes them useful in newly constructed homes as they can be placed virtually anywhere.
When the thermostat detects cold water, the draft inducer pulls fresh air into the burner.
The pressure switch then verifies that there's enough airflow for combustion.
Next the hot surface ignitor heats up and ignites the burner.
The flame sensor monitors the burner to confirm that there is a flame.
The burner runs until the water in the tank reaches the set temperature.
After the burner shuts off, the inducer will stay on for several minutes
to purge the system of exhaust gases.
Power vent water heaters are similar to high efficiency furnaces.
If any one of the safety switches trips or is faulty, then the water heater will shut down.
It will attempt ignition several times before going into a hard lockout.
The water heater will use flashing lights as codes to describe the source of the error.
It's best to check your manual to see what these codes mean.
You can learn more in the videos linked in the description.
Hopefully this has given you a better understanding of how water heaters work.
For more troubleshooting on water heaters, furnaces and appliances
then subscribe to our channel.
And if you need help, you can call or visit an AMRE location
to talk with our knowledgeable staff. Thanks for watching.