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Fixing Commercial Ovens: Not Cooking Evenly

All the thermostats have a capillary tube with a bulb attached to the end of it.  This is the part that senses the temperature in the oven.  The bulb is attached to clips inside the oven.  If the bulb is not put back in the same place, i.e. it’s just stuck in the oven cavity and left hanging, then the thermostat will run “wild,” meaning the oven cooks unevenly.  Commercial Oven Thermostat w/ Capillary Tube

Remember to get that bulb back into those clips no matter how hard it may be. 

If your oven is running wild check and make sure the bulb is installed properly.  Another reason for the oven running wild is that the thermostat is totally defective and in this case must be replaced.

There are two types of gas thermostats: BJWA and FDO type thermostats.  BJWA thermostats are the most common type and older ones can be identified by the nickel sized hole on the front where the knob attaches.  (See picture above)  However, newer BJWA thermostats may not have that hole.  FDO thermostats are usually found on pizza ovens and can be identified by the disc with numbers on it that sits behing the knob stem.

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About Greg McGuire

Greg has blogged about the food service industry for years and has been published in industry magazines, like Independent Restaurateur and industry blogs like Restaurant SmartBrief. He lives in Colorado with his wife and two sons and enjoys reading, live music, and the great outdoors.

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  1. lp oven is not burning right, yellow flames shooting up at the air valvue of the burner. other oven is fine.?????

    • Sorry for the delayed response. Our service techs on-site believe it could be a faulty regulator, a clogged flue or buildup on the pilot orifice. If you can call Tundra Restaurant Supply at 1.888.388.6372 and describe the issue in more detail they may be able to better pinpoint the issue and get you the parts you need for your unit.

  2. Hi, I have a a question.

    1)how would you identify the model of a royal gas range? The best description I can give is it seems to be all one piece and is about 8″ has 4 top burners with a flat top grill and 2 low ovens and a shelf above all of the unit.

    Thanks in advance.

    • Under the oven doors is a kick plate; remove the kick plate and that is where you will find your model and serial number. There could also be a data plate somewhere on the back of the unit where gas/electric connections are.

  3. This might sound crazy but I caught my propane oven on fire and now after I cleaned it the pilot light on the broil part is on but my oven won’t heat up. What should I do ????

    • Hi Chelsey,

      It could be the Pilot Safety Valve or the Thermostat. Without knowing the specifics of your machine, I would recommend calling the manufacture of your unit and asking for their technical department to help with troubleshooting.

      – Paul
      Tundra Team

  4. When using the oven on my Imperial range, the flame stays the same at all settings, so the oven never heats up enough to cook anything. what gives?

    • Hi Terry,

      The most likely cause would be manifold pressure and orifice sizing. If the unit is not mixing the right ratio of oxygen to fuel it will not burn blue and clean. These adjustments require specific tools and training and should be preformed by a qualified technician.

      – Paul
      Tundra Team

  5. Quick question – I have a Garland Residential Gas Stove. There is a heavy porcelain enamel shelf/plate on the bottom of the oven. There are three holes (about one inch each in diameter). Do those holes go to the front of the oven or the back. We just cleaned the oven, and there is no mention ANYWHERE (thank you Garland) about which way the shelf should go in. I think we had the holes incorrectly at the back of the oven, and the temperature gauge seemed to be off. We have placed the holes to the front of the oven and are hoping this has solved the problem, but would love a confirmation from anyone who knows ovens. Any help in that regard would be great. The pilot light is at the front of the oven.

  6. Hi Cerys,

    Without seeing your unit, it’s tough to say. I’d suggest you go to the Garland site directly to locate your exact owner’s manual, or to talk to one of their experts.

    – Paul
    Tundra Team

  7. My propane oven goes out and relights every few seconds. The pilot stays lit…

    • Hi Robert,

      It sounds like you have an ignition problem. I’ve seen this with models that have ignition control boxes and spark igniter. There could be a number of issues that would lead to the unit doing this. The incoming and manifold gas pressures need to be checked as well as orifice size verified for your altitude requirements. Also, it could just have an issues with the control box or igniter. These are very picky units when it comes to getting everything dialed in correctly and should be performed by a licensed technician.

      – Paul
      Tundra Team

  8. hi Paul

    I have an imperial ir 36 gas oven. Upon ignition the flames from the burner ribbon(which is in the center of the oven) roll both left and right from the center and extend up into the baking chamber. I put a new gas regulator in and set gas pressure to 5″WC. I also replaced the gas safety valve and I cleaned the burner ribbon. The second problem I have is black soot(I assume unburned gas) contaminates product cooking in oven. After a few minutes the flames subside and I no longer get soot. I have tried adjusting the air mixture on the burner ribbon and nothing has worked. The only thing I have not done is replace the thermostat. Any suggestions???

  9. Hi Paul,

    It sounds like you have the wrong burner orifice in there, but I would call Imperial’s technical service to get the correct size: 800.343.7790

    – Paul
    Tundra Team

  10. We have a Royal three burner two thermostat grill pilot light stays lit but burers go off and we have to tour knob off then restart. We are using LP gas. Any ideas

    • Bill,

      Several issues could have those symptoms. To check the thermostats, you would need a grill thermometer to find out what temperature the burners turn off at compared to the thermostats settings. If they turn off within 50 degrees of the setting, they might be able to be calibrated. You might need the help of a qualified service technician to do this properly.

      – Paul
      Tundra Team

      • Thank you

        One other thing I noticed is they are on propane and the grill is at the end of the line. There is a 80 gallon hot water heater and a new gas deep fryer in front of it also. Could that cause a problem? The general manger said they just changed propane suppliers and this started happening I told him to have the propane supplier make sure they have the correct pressure coming in to the building? Not sure if this could cause this issue.
        Thanks again

        • Bill,

          That would be something to check for sure. I’ve had a lot of customers with similar problems on Food Trucks, in their case they needed a new regulator on their tanks.

          – Paul
          Tundra Team

  11. I have a dean deep fryer and the pilot light works great but the burners don’t kick on until the knob gets turned to 400 and goes back to pilot if I turn it back down below 380. would that be a bad thermostat?

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