Oven Gas Safety System | Desiree's O'Keefe & Merritt Stove

My vintage gas stove has safety systems for the oven, and another one for the broiler.

Safety systems mean, for any reason, if the gas flow to the stove stops while the oven or broiler were on, when the gas flow is re-established to the stove, raw gas does not quickly fill up the oven or broiler cavities. Lots of raw gas in an enclosed space can cause an explosion if it is suddenly ignited by a flame or spark.

Prior to that time, when ovens were light with a match, stove operators would open their oven doors, say to check on their baking, see/hear the main burner was out and try to relight the oven, not realizing the oven was still full of raw, uncombusted gas. Boom!

In my stove, one set of safety system components are for the oven, another for the broiler;

safety valve
pilot burner
thermocouple.

Safety valve: After the oven thermostat valve is turned on, gas flows thru it towards the safety valve. It the thermocouple is working and sending the tiny voltage to the safety valve, that valve stays open, letting the gas pass thru and flow to the oven burner. The pilot burner ignites that gas and the oven is afire, ready to do its job.

Pilot burner: The pilot burner flame is like the canary in the coal mine; an indicator. If the pilot flame goes out, it’s possible the entire stove stopped being fed gas.

Thermocouple: It sits right next to the pilot burner because it is supposed to be heated by the pilot burner. The thermocouple is like a battery. When it get hot, it generates a tiny voltage and sends that to the safety valve.

If the opened safety valve says, “

“The thermocouple isn’t talking to me. I’m stopping gas flow to the oven. When the gas starts flowing again, and the pilot burner is talking, someone is going to have to push the red button for me to open.”

Yup. It says all of that. 😉

When a vintage gas stove is disconnected from the gas supply, whether for repairs or transport, you can now guess what the safety system will do

Many people who get their new-to-them vintage gas stove ponder why the oven won’t work. A closed safety valve is a very common cause.

OK. Nice to know. Duly noted.

The problem is sometimes the entire safety system fails, the oven doesn’t turn on or doesn’t stay on, even the safety was manually opened.

Now what?

I want to know how to troubleshoot the system myself. There are a few good reasons. There are no vintage gas stove experts within any conceivable distance to me now. I’m in the center of Vermont. And even if there was a vintage gas stove expert nearby, I couldn’t afford to get him/her together with my Lucy. But, as matter of pride, I’ve studied my stove’s systems long enough to understand how it works. I can do this!

A problem may be simple to fix. A tip that Steve Sansone keeps reminding people to do – check the clock. If your OKM stove has one with a CSM dial [Clock, Set Manual], make sure it is set to Manual, or the oven might not turn on when expected to. OKM’s Automatic Oven Timer. Note the “CSM” which stands for Cook, Set, Manual. One day, after a good brain rest, I may try to sort out the “C” and “S” options.

Another possible problem. Dirty, clogged or corroded thermocouple or the pilot burner. Over time, those things can get coated with debris, or degrade and need TLC or replacing.

If I see that, I could try using a fine wire brush to remove buildup from the thermocouple probe (when the oven is off, of course!). It’s also possible the pilot burner is a bit clogged so it cannot produce the healthy blue flame needed to keep the thermocouple bathed in that nice blue flame.

In my stove, the pilot and thermocouple are placed in the back of the stove, kinda underneath the oven burner, that pair may be hard to reach. Strong abdominal muscles and long arms help.

I learned the oven pilot burner in my stove was actually corroded! I thought that might distort the flame, reducing the flame’s ability to heat the thermocouple. Sad, worn pilot burner.

The oven’s pilot burner can also be a potential problem source, especially if the stove has recently been moved. There is a tiny orifice insert inside the pilot burner’s base that contains a near microscopic opening that the gas must pass thru. So tiny is this opening that any particle could impede or block the flow. If a particle is large enough to block the opening, your oven pilot flame may not be big and hot enough to make the thermocouple happy. When that happens, your thermocouple won’t talk to the safety valve and the safety valve will close the gate that lets gas flow to the oven burner.

If your oven is not acting proper, it’s good to check that your oven pilot orifice is clean and that tiny opening is wide open. As the pilot orifice is made from soft metal and is a precise size, try using a 28-30 gauge copper wire to clear the opening. The wire must pass thru the opening easily to avoid distorting the opening.

Next stuff to check

How about the thermocouple? It’s like a battery. When hot, it can make electricity, just enough to signal to the safety valve. But like a battery, it can weaken, then die. If that happens, it needs to be replaced. My stove takes a 48″ long thermocouple. The long rod end gets mounted next to the pilot burner. The other end snakes out from the oven and up to the safety valve.

A fully charged thermocouple produces approximately 30 millivolts when heated by the pilot burner. That tiny voltage is what is needed to keep the safety valve open.

Resetting the Oven Safety System

If the safety valve is in good working order, I just need to make sure the pilot is burning a happy little blue long enough to heat the thermocouple. The safety valve is still closed because the thermocouple signal only holds the valve open. the only thing I will need to do is manually push in the red button long enough to allow the gas to flow to the oven burner, where the pilot will ignite the entire burner.

The cryptic instructions are printed on the inside side of the broiler door! (Left side)

When I’m doing serious gas work on my stove, I’ll shut off the stove’s gas supply, so I may reset the safety system half a dozen times. Easy to remember the steps. But when I go months or years without doing that sequence of steps, I refer to this list.

Steps to resetting oven (or broiler) safety system

Lucy’s two safety valves are just under the cooktop. So I prop it up. I also open the oven and broiler doors to reach those respective pilot burners.
Light all the pilot burners. It is important that the oven and broiler thermocouples sensors are bathed in the flame.
Turn on the oven. The gas will flow from the oven thermostat control to the safety valve. It will stop there, if safety valve is closed. I need to push in the red button on the oven safety valve to manually hold it open. Keep the button pressed in until the gas has sufficient time to flow to the oven burner and ignite.
I can then release hold on the red button. The button will return to its original position but the valve should remain open. It will stay open as long as long as the pilot flame heats the working thermocouple, the thermocouple will signal to the safety valve to remain open as long as gas flows to the pilot burner, which is expected to be 24/7.

Troubleshooting

Suppose I try those standard resetting steps and the oven still doesn’t light or won’t stay lit.

Thermocouple: The mostly likely failed component is the thermocouple; the least expensive and readily available at most hardware or stove/furnace suppliers. It either can no longer generate the required voltage or it’s not being heated enough by the pilot burner. First, I’ll check the pilot to if I can tell if the flame is truly bathing the thermocouple sensor end in flame. I might even crank up the pilot valve a tiny bit to see if that increases the flame size. Next, disconnect the end that connects to the safety valve. I’ll use my multimeter to see if the thermocouple can generate 30 millivolts. If the voltage is below 25, replacement time. If I need to replace the thermocouple, I get the 48″ length.

Note: If I order a new thermocouple, I will test it as soon as it arrives. I’ve heard of folks going through the trouble of installing new thermocouples that turned out to be dead.

Clock: Chances are my clock’s setting isn’t a problem, but I’ll glance to make sure it’s set to “M” (manual). On manual, the solenoid valve is supposed to be open.

Safety valve, oven thermostat: The other components that can fail (oven thermostat or the safety valve)… well they are not inexpensive. They are far less likely to fail, but after 70 plus years, anything can fail. However, their roles are simple. They are valves, gates that should open/close. The concept of testing them is logically easy., although the practicality of messing with gas plumbing is best left to the professionals.

Safety valves and has oven thermostats for vintage stoves are specialty items sold mostly by suppliers that sell vintage stove parts, HVAC or restaurant equipment. There are also sellers on ebay. Thus is the risk of owning a vintage item.

Misc: The remaining possible failure points in the above list I’d leave for lowest concern. I cross my fingers and hope moving the thermocouple and pilot burner a tiny bit closer together does the trick! 😀

Addendum #1 – Modern Safety Valve

Vintage gas safety valves: My Lucy and most of the OKMs I rescued that had safety valves, there Robertshaw models… Their job was to control the flow of gas from the oven thermostat to the oven burner, and from the broiler valve to its burner, if the stove had a Grillevator broiler.The safety valves did not control any of the little pilot gas flows.

Modern safety valves: The more recent gas safety valves are constructed to handle the oven/broiler main gas and pilot gas flows. Chances are when I switch to propane, I’ll eventually install updated safety valves for the oven and broiler. That will require modifying the gas plumbing lines! Oy vey!

This is the model for my Lucy. Robertshaw 1720-008 magnet head and the Robertshaw 1710-112 body for 7/16″ gas line.