If you determine that your oven thermostat won’t regulate the oven temperature and the heat just keeps increasing, typically you have to replace. Thermostat repair is not really a DIY project, unless you have very specialized equipment.
The only useful DIY info I can share with you is sharing how I found the proper replacement thermostat and how I installed it. Also it is possible to send in a non-functional thermostat and get it rebuilt. That could be a better option if you cannot find the proper update to your model.
A critical component of my stove that didn’t seem to work right since I got it was the oven thermostat. Because I didn’t have any OKM stove documentation yet, it took me a while to realize that O’Keefe & Merritt stoves didn’t have O’Keefe & Merritt oven thermostats – they had RobertShaw brand thermostats.
Knowing that really helped reduce my confusion when reviewing search results for how the things were supposed to work, how much new ones cost, how many different models there were. Ah, the famous Robert Shaw thermostats. Nice, purely mechanical oven temperature regulators – no electrical hookup needed.
So back to my problem. My stove came with a sad, half broken Robert Shaw BJ model oven valve and thermometer. How did I know? It did allow gas to flow when turned on, and it could stop the flow when turned off. When lit, the burner flame was low. Basic testing by PG&E and myself indicated the thermostat itself leaked gas from the front stem and near the back of the unit. Possibly enough gas was leaking from the thermostat to impact the amount getting to the burner? It’s biggest failure was the thermostat could not regulate the temperature. That meant the temp would continue to climb higher and higher, no matter what the dial was set to.
Pricing RS Thermostat Repair Options
Surprisingly, these little mechanical stove jewels and their updated cousins are still available but at a ‘sit up and notice’ wide price span of $150 – $650! Well ain’t that’s just grand. Best prices currently are at Repco in Texas Make sure to call them; ignore the website inventory.
My other option – send it out to the same folks to rebuild. That was actually no cheaper! The thing was, getting my thermostat rebuilt meant I would get the right/original thermostat for the oven. If I ordered one I’d have to make sure to get the right model. RobertShaw has been updating and expanding their line of BJ thermostats since at least the 1940s.
But the oven gods had smiled upon me. A seller on ebay had a small collection of new RS oven thermostats for $85! Eighty five dollars and free shipping! I figured it had to be ones I couldn’t use. So I searched for all possible online sources. Incredibly, I actually found similar replacement models ranging from $200 – $600. That made it even harder to forget the $85 dollar one. 🙂
The only problem – assuring what was for sale would be a proper replacement. My stove’s model was a “BJ”. The ebay models I found for sale at that time were BJWAZs; BJ replacement kits with VC4500-005, -006 units.
Huh?
Don’t ask me. I didn’t name the things. But know this… There are a lot of specifications to these thermostat controls including;
- switch position (left/right)
- outlet position (left/right)
- outlet diameter (1/4, 3/8, 7/16)
- capillary length (36″, 48″, etc.)
- dial rotation (left/right)
- temperature range
- rear housing (down/right/left)
- switch terminal connections
- mounting characteristics
- housing dimensions
So it’s important to know what model replacements will work for your stove. Here’s a link to a very helpful RobertShaw pdf. It’s a little much to take in at first. If you use a little patience and learn their lingo, it will really help you understand the thermostat market.
After lots of research, it seemed like the BJWAZ would really work as a replacement in my stove, so I finally ordered it, made a small piping extension since the outlet was on the left side instead of the right side, installed it, turned it on…
It worked!!! It worked beautifully, accurately. Hot damn!
My old BJ and new to me BJWAZ
First and foremost, I wanted a suitable working thermostat. I began to learn that the famous BJ model design had advanced. Additional components were added over time. Modifications came with extra letters like BJ-S, BJ-WA, BJ-WAZ, then the letters were swapped out in favor of numbers like 4300, 4350, 4500… Looks like the current favorite is the 4500 series.
“4500 Series Domestic Gas Thermostats
The 4500 Series (BJ) kits are designed to provide the service technician “one call” field replacement of the vast majority of BJ and competitive variations of this widely used control. Kit includes a 4-position dial which allows the control to be mounted in any of the four mounting positions while retaining the correct “off” indexing. Outlet position on the control is down – 6 o’clock, but may be rotated to 3 o’clock, 9 o’clock or 12 o’clock (instructions included). Dial guide is orange color coded on old control and on the new kit controls.”
However, the part about the thermostat that I sort of grew attached to was the BJ thermostat knob. It’s the only part that is designed to interface with the user. The BJ one had a pleasing domed which made it nice to grip. All the lettering and numbering paint was gone, but I had planned to fix that.
I figured when the replace thermostat came, I’d just swap the new knob so I could keep the domed one.
Phooey. The knobs were not at all swappable.The thermostat mechanisms were very different. One rotated CW, the other CCW. The stems that inserted into the knobs were very different. *Pout* So one day, when approximately $150 – $200 is burning a hole in my credit card, I’ll send my old BJ to Repco to be recharged.
Fruitless fun
This is a RobertShaw BJ thermostat, the model that was original to my stove. I took photos while taking it apart. I even made new gaskets for it to make it stop leaking gas. However, no amount of tweak, lube, cleaning, gasketing, etc. would get the thing to work.
Time to play with the thermostat! Now, I was told, advised, warned that these thermostats were not DIY items. Not! Not! Not! No one said why, but all the experts made that fact clear. OK. Thanks for the heads up.
Did that stop me? Nope. I figured I had nothing to lose. Besides I HAD to give it a shot before laying out hundreds of dollars to buy a replacement for a feature I didn’t really need. I already had a great countertop digital microwave/convection oven.
Of course, there was also that curiosity thing. 🙂
So I opened it up. Such fun curious internals. Lots of bits, pieces, gizmos and such. First thing was to identify leak locations. I made gaskets for the unit that successfully stopped the gas leaks. I cleaned, lubed, adjusted everything I could. After that session, the burner flames were larger, which seemed great! Although I soon discovered the oven would get nice and hot, then hotter and hotter. It couldn’t hold a set temp. It’d just continually burn at max output. A pretty dangerous behavior – indicating the thermostat still didn’t work.
But at least I explored the inside. In fact, I accumulated and explored three or four more RobertShaw thermostats, all of which didn’t work. I still want to know what it takes to rebuild these things.
Years later, I learned why. If it wasn’t already totally dead when I got the stove, I would have killed it by going too far in the disassembly.
You see, that thick wire that comes out of the back of the BJ and goes into the oven is not really a wire. It’s a tube, a tube filled with a highly temperature-sensitive substance, like gas or mercury. As the temperature in the oven increases or decreases the bulb on the other end of the tube (the bulb that sits inside the oven) mechanically expands/contracts. That mechanical change impacts the thermostat’s internal mechanisms. Once that back part is opened, the substance inside the tube escapes. And you cannot put the genie back in the bottle. Only a professional shop can – Repco, in Texas. They specialize in rebuilding oven thermostats.
