Here's where I was going when I mentioned the thermo-couple sensing the drop in temp....
"A thermo-couple sensor detects when the temperature of the water drops and sends an electrical impulse to the thermostat control. The thermostat causes the burner to light and bring the temperature of the water back up to the temperature setting on the thermostat."
The "piezo" switch needs mechanical input in some way, that is, if we're dealing with a piezo SW per-se. However, it's quit possible, there is an electronic ckt that triggers the ignition or lighting of the gas, instead of a piezo, upon receiving the call for heat?
After giving this more though, I'm just trying to rationalize the process.
Pilot stays on constantly, temperature probe on gas valve controls call for heat, the piezo is just like an electric spark lighter, you push button to send a spark to pilot.
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the way they work is the pilot generates 30 milivolts of electricity
Originally Posted by catmanacman
Can you expand on this? Thanks.
You do not understand the operation of you unit.
Do a search for your manual online, or read it if you have it.
Your gas valve is the control over complete operation of the fire on that unit; on, off or pilot only operation.
The piezo is strictly an ignition(spark) just like on a barbeque.
The thermocouple is the safety, along with an over temp safety on this unit, that provides a millivoltage to hold open a magnet in the gas valve. This voltage is created by the heat of the pilot flame burning on the thermocouple.
If you read the lighting instructions, you must hold the control valve down for 30-60 seconds while lighting the pilot. This is to allow enough time for the heat to generate the voltage to hold that magnet.
You are making things way to complicated. You unit works without the need for house power. You have what you wanted, unless you are on a well and then you need power to deliver the water.
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from an excerpt by Paul Jacob in Sun City, AZ
Your thermocouple is is the pilot flame. Your water heater's thermostat is a mechanical switch. As long as the pilot is lite. The thermocouple generates voltage.
Originally Posted by Abuello
I don't remember the exact physics, but the energy from the flame when run across a thermocouple, generates a very small voltage (30 millivolts) to ground. This very small amount of power can be used for very simple controls like opening a gas valve when a mecahnical thermastat closes. ITs' also used as a simple flame detection system. if the flame goes out, the controls lose power and the gas valve shuts.
Originally Posted by Abuello
SO the water heater generates it's own electricity. The downside is that you have the continous gas useage and the need for a open draft vent where you are constantly losing heat to the flue. That's why the eneryg factor is about 0.56, when the burner istself is around 75% efficient. You have big standby loses from the flue as well as the insulated tank.
Thanks for all of your replies. I think I have it figured out. As "beenthere" has mentioned, the Piezo is there to re-ignite the pilot at such time, it is needed. This unit still has a pilot flame and thermo-couple to control the gas valve. As another respondent mentioned, had I some type of full auto-light system , it would have required a dedicated electrical connection. A power outage would have put me without hot water. I think this is how it goes.