How does a gas log safety pilot work?
Aside from the electronic ignition systems, the basic premise for the safety pilots used on gas logs is the same as those used for decades with wall heaters, hot water heaters, and nameless other gas appliances.
How do you light a gas log safety pilot?
You turn the control knob to the pilot position, push the knob in, light the pilot with a match, then hold the knob down for 30 seconds or so until the pilot stays lit by itself. Once the pilot light will stay lit on its own, you can then move the knob to the "On" position. For manually operated gas logs such as the one pictured to the right, this will turn the logs on. For remote controlled gas logs, this will put the valve in the necessary position for the remote control to actuate the burner.
What if the pilot will not stay lit?
If you cannot get the pilot to light at all, meaning you hold the button down in the pilot position and hold a match up to the pilot and nothing happens, then either the valve is bad or something is abstructing the gas from coming into or going through the valve. If you can get the pilot to light with a match, but it will not stay lit on its own after holding down the knob for 30 seconds, then put the knob back into the off position, wait 5 minutes and try again. If it still will not light, then something is definately wrong and you should have a professional check it out. This page is not meant to be a trouble-shooting guide for gas logs, but in general, if you cannot get your safety pilot to stay lit, It could be that the pilot flame needs adjustment, the thermocouple has gone bad and needs to be replaced, the entire valve has overheated and must be replaced, or something is abstructing the gas line. In any case, it is probably time to seek the assistance of a professional. Any plumber or heating and air conditioning service man who deals with gas appliances with a safety pilot should be able to help you.
How does a safety pilot actually work?
Although most of us have learned how to light one of these things at some time or other, few of us have any idea as to how this ingenious little safety system actually works.
So here is a brief, but hopefully useful explanation of how gas log safety pilots work so you can decide if it is something that you want or need. You may also find this information helpful for any other device that has a similar safety pilot.
Gas Logs that have a safety pilot have a valve body that is attached directly to the burner. This valve body that has 2 separate valves inside that control the gas: The valve to the main burner and the valve to the pilot flame. When the pilot is lit, the flame directly hits what is called a thermocouple (or thermopile). The thermocouple is the ingenious device that makes the whole system work. The physical properties of the thermocouple are such that it actually generates electricity when there is a great enough difference in temparature between the tip of the thermocouple and the base. If the pilot flame is too hot, then the entire thermocouple gets hot and there is not enough temperature difference to create a current. If the pilot flame is too low or not coming into direct contact with the thermocouple (or simply blown out), then there is not enough heat to generate a current. This is why the proper adjustment of the pilot flame is necessary for gas appliances that have a safety pilot.
Now, on to how the pilot system works. The electricity from the thermocouple is used to power an electromagnet that holds the pilot valve open, thus allowing the pilot to stay lit by itself. The amount of electricity needed must be within a certain range of millivolts in order for this to happen. If there is not enough electricity (or no electricity) being generated, then the electromagnet no longer functions and the pilot valve shuts. When you turn the knob to the pilot position and push it in, you are in fact manually opening the valve to the pilot flame. Once the pilot gets the thermocouple hot enough, the electromagnet engages and keeps the valve open. This is why you need to keep the knob depressed for about 30 seconds.
After the pilot is lit and stays lit on its own after releasing the pilot know, you can then turn the knob to the "ON" position. With manually operated safety pilots, turning the knob to the on position will light the logs and you can adjust the flame height using the control knob. With remote controlled systems, turning the knob to the on position simply puts the main valve in a position to be opened and closed buy whatever means the remote control uses. In the case of a remote controlled valve, some will have a battery operated device that opens and closes the valve to the main burner, thus turning the logs on and off. More sophisticated systems (called variable flame remotes) will have a battery operated motor attached to the flame adjustment knob that will allow you to adjust the flame height as well.
The main burner valve is designed such that if the pilot valve is closed, no gas can flow through the main valve, even if you have it in the on position. So as long as the pilot light is on and heating the thermocouple properly, the system is operational and gas can then be allowed to pass through the main burner valve. If the pilot light gets turned off or blown out (or in some cases gets too hot), then all valves are closed and no gas can pass through the system.
When the main burner is turned on, either by a remote controlled unit or by manually turning a knob, gas flows through the main valve and comes out the holes in the burner. The flame from the safety pilot is positioned just above the first several holes in the main burner, so when gas flows out of the main burner and reaches the safety pilot, it automatically ignites.
So again, if the safety pilot is not lit (or for some reason the safety pilot gets blown out), the system automatically closes both valves so that no gas will flow through either valve until the safety pilot is re-lit. This prevents the system from allowing gas to flow freely into your home at any time in the event that the safety pilot blows out, or someone turns on the gas to your fireplace without lighting it.
source: http://www.hansenwholesale.com/gas-logs/how-safety-pilot-works.asp
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