o keefe and merritt oven safety valve factory

Safety valves. It took me a little while to figure out how they worked, what their true purpose was.  But let’s start with the outside of the stove. There’s a “CP” logo. That stands for “Certified Product” and is a trademark by the American Stove Makers Association that ensures that your stove meets certain high standards, like the stove’s oven/broiler safety systems. A highly respected and knowledgeable vintage stove sage I know (Steve S.) said about 20 criteria must be met to earn the designation.My OKM vintage gas stove has safety valves and connected thermocouples for a safer operation of the oven and broiler.

The Robertshaw TS Series thermomagnetic safety valve is a control used to cut off the flow of gas to the burner in the event of a pilot outage. The magnet assembly is energized by voltage generated by a thermocouple that is heated by the pilot flame. When this flame is extinguished, the thermocouple voltage decreases until a spring overcomes the magnetic force and loses off both the pilot and main gas (the older valves just shut off the main burner gas). This control can be used for commercial and residential ovens, infrared heaters, chicken and pig brooders, recreational vehicle gas appliances and many more applications requiring automatic safety valves!

What it means is if, for any reason, the gas flow to the stove stops while the oven or broiler burners were on, in addition to the burners going out the pilot flame would go out. That would cool down the thermocouple probe which sits in the pilot flame. When the thermocouple is not hot enough, it signals the safety valve to close, which blocks gas from flowing to the burners.

WHY?Prior to safety systems existing, when these stoves were being produced, gas distribution was not always reliable. Sometimes, the gas supply would die out, shutting off the flames. Then after a little while, the gas would come back on.

Unlike the cooktop burners, the oven burner is hidden. If say, a bread baker were only using the oven at that time the gas supply stopped then started again, she or he might not have realized what happened. It was possible the baker might open the oven to check,  realize the flame had gone out and try to relight the manually lit oven with a match.

With a safety system, when the gas flow was re-established to the entire stove,  the safety valve would have prevented the raw gas from filling up the oven or broiler chambers because the valve closed when the pilot light went out.

These days, gas distribution is pretty reliable. Most often safety valves can seem to be a problem for three reasons: a) after the gas has been shut off from the stove (so the stove can be safely repaired or relocated), b) when the thermocouple bimetal’s charge dwindles and dies, c) when the safety valve loses its magnetic charge and cannot stay open.

When my gas stove was moved into my kitchen, I needed to perform a manual reset of the two safety valves so I could test the oven and broiler. When the stove was disconnected from the previous owner’s gas line, that killed the pilot flames which cooled the thermocouples which closed the safety valves.

Each time I worked on my stove’s major systems, I’d shut off the gas to the stove. To restart the oven and broiler burners, I’d have to manually reset the safety valves if I wanted the oven and broiler to auto light again.

Made sure the pilot flame is on and the thermocouple probe is in that flame. The heat causes the thermocouple to charge and send a signal to the safety valve. The signal cannot open the safety valve, but it can only keep it open. If the pilot is not lit, I’d light it and wait about a minute for it to warm up enough to signal the safety valve.

Pushed in and held the red button on the safety valve. Pushing the button manually opens the safety valve, allowing the gas to flow to the oven/broiler burner. Once the gas flow reached the burner, the pilot flame would ignite the oven burner. Small happy dance.

Released the button on the safety valve. When everything worked properly, the safety valve would stay open, because the thermocouple sent a signal for it to stay open. Big happy dance. If the oven burner shut off after that process, I assumed the thermocouple signal was too weak to keep the safety valve open. Time for a new thermocouple. Pout! Or the safety was on the fritz. Major $$$ pout!

If you have a multimeter with a DC volt scale, you can use that to test your thermocouple’s charge. But don’t ask me how. I’ve no meter nor knowledge on such things.

There are many different safety valve model for major gas appliances like stoves, water heaters and furnaces, but they all have the same purpose – to prevent raw or uncombusted gas from leaking. Their designs and features have evolved over the years. If you’re trying to find a replacement safety valve for your stove, you don’t have to necessarily get original unit.

But you do need to make sure the replacement valve meets all the critical requirements. For example, the gas line openings need to be the match the diameter of the gas lines in your stove, it needs to have correct port for the thermocouple, it needs to fit the opening of the previous unit, etc. There are workarounds for most of that, but it involves plumbing adapters, additional gas lines and/or plumbers.

When my old gas furnace safety died, troubleshooting pointed to the safety valve as the trouble. I disconnected it and took it to a local appliance parts shop. Thankfully, the owner recognized my old no-longer-available furnace safety valve and knew which updated model would work.

The Robertshaw® 1720 Series Thermomagnetic Safety Valve is a control used to cut off the flow of gas to the burner in the event of a pilot outage. The magnet assembly is energized by voltage generated by a thermocouple that is heated by the pilot flame. When this flame is extinguished, the thermocouple voltage decreases until a spring overcomes the magnetic force and closes off both the pilot and main gas. This control can be used for commercial and residential ovens, infrared heaters, chicken and pig brooders, recreational vehicle gas appliances and many more applications requiring automatic safety valves.

My vintage gas stove has safety systems for the oven and broiler. I thought it was of one of the things  that CP (Certified Performance *) trademark of the Gas Appliance Manufacturers Association is about. “CP” stoves have a long list of safety and performance features which evolved over time. (see page bottom)

As far as I could tell, it meant, for any reason, if the gas flow to the stove stops while the oven or broiler was on, when the gas flow is re-established,  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.

OK. Duly noted. The problem is sometimes the entire safety system fails, the oven doesn’t turn on or doesn’t stay on. Many people don’t understand why or how to fix it. They just know their oven or broiler won’t light. Very frustrating. Playing with gas stove problems is not for the faint of heart. Playing it totally safe means locating a vintage stove expert, which in most circumstances is NOT your standard appliance tech. But these stoves are not that complex. If you’re confident in understanding a few basic concepts and respect with gas can do when you are too sloppy, you might be able to either fix the problem or explain enough to a plumber or gas technician that they can fix things.

At the page end is a set of drawings that might help you understand what is involved in a working and non-working safety system.  There are several separate components that have to be working. If the oven or broiler won’t light or the oven is not keeping the right temperature, , a conversion between NG and LP, one of more of those components might have failed.

The problem may be simple. Greasy or ashy buildup could be causing a problem. The standing pilot and thermocouple that sits right next to it, can over time, accumulate gunk. After all, they’re sitting inside the oven near the oven’s main burner. Who knows what gremlin dirt may have been deposited when the door is closed?