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Replacing Gas Safety Valves

There are many different types of safety valves. These are the most common types:

  • FMDA
  • BASO
  • TS
  • Combination Type

1. The FMDA safety valve is the only type with the thermocouple permanently attached to it.  This means the thermocouple cannot be replaced; the entire safety valve must be replaced if the thermocouple fails.  The easiest way to identify an FMDA type safety is a ½” diameter red button on the bottom of the valve.  You must know the gas pipe size and if the pilot tube is an “in and out” or an “out only.”  An “in and out” safety valve has two threaded holes at the top of the part, one for gas for the pilot to come in and one for gas to go out.  An “out only” safety valve has just one threaded hole to connect gas for the pilot to.

FMDA Safety Valve

FMDA Safety Valve

2. The BASO safety valve can vary in design depending on the piece of equipment it is on, so it is important to know the brand name, model and serial number of the piece of equipment to get the correct safety valve the first time.  The easiest way to identify a BASO valve is by the 15/16” diameter red pilot button.  The thermocouple is separate from the safety.

BASO Safety Valve

BASO Safety Valve

3. The TS type safety valve is the only one that can be rebuilt.  It is similar to the FMDA and BASO types in that it has “in and out” or “out only” pilot tubing, so you must know what is in your equipment.  A rebuilt kit is available in both and it is not necessary to replace the body unless it is damaged.  The body has no moving parts in it.  The easiest way to identify the TS safety is by the 5/8” diameter red button.  The thermocouple is also separate from this safety, similar to the BASO.

TS Safety Valve

TS Type Safety Valve

4. Combination safety valves come in three different styles:

  • 120 Volt Type
  • Tubing Type
  • Millivolt Type or 24 Volt Type

A combination valve is a gas valve with the safety built into it.  Most combination valves are found in fryers.

Combination Type Safety Valve

Combination Safety Valve

How to determine which type you have:

  • If there are two wire leads coming out of the valve then it would be the 120 volt.
  • If the wire leads are screwed to the top terminal block, and two tubes are coming out of the top of the valve, it is the tubing type combination safety valve.
  • If the wires screw into a terminal block it would be a mulitvolt type.If you are not sure, just provide the brand name, model and serial numbers.

Every combination valve uses either a thermopile or thermocouple.  The most common is a thermopile, and there are two different thermopiles:

  • Screw-in type
  • Two-lead type

The screw-in type screws directly into the body and the two-lead type has a terminal block on the combo valve to directly screw into.


21 Responses to Replacing Gas Safety Valves

  1. Andrew C. August 6, 2009 at 10:09 am #

    The FMDA Gas Safety Valve does not have a thermocouple permanently attached to it. What you are mistaking for a thermcouple is a capalary tube. The capalary tube is permanently fixed to the gas valve because it is filled with mercury. When the end of the tube which is heated by the pilot flame and gets hot enough the mercury travels towards the gas valve completing the connnection to allow for the magnatie to hold. In turn with the maganite holding gas flow is allowed when requisted by the thermostat. The action of a thermocoulpe / thermopile and a capalary tube are diffrent but accomplish the same task.

  2. Chip December 17, 2009 at 5:48 pm #

    Andrew, FMDA valves do not use mercury.

  3. mike hofmann December 25, 2011 at 7:57 pm #

    I have a wolf range and the oven pilot stopped working. i have obtained a new FMDA type safety valve. do these valves have a conversion to LP. I suspect that they are shipped for natural gas.

    • Tundra January 3, 2012 at 7:04 am #

      Hi Mike,
      Sorry for the delay I just got back from vacation. There is nothing you need to do it will work on either propane or natural gas.

  4. Tim January 7, 2012 at 3:25 pm #

    Is there any replacement for a FMDA without the mercury. I have a wolf and have to replace the safety valve about every 6 months

  5. chuck April 30, 2012 at 11:32 am #

    i am considering buying a used convection, which on craigslist looks clean, but the seller says the blower works intermittantly…but the oven reaches proper temp…the purpose of the oven is to bake artisan breads…what do you think…easy repair?….can i bake bread without the blower?

    sincerely chuck

    • Tundra May 3, 2012 at 10:33 am #

      Hey Chuck,
      Something like a convection oven where the blower only works part of the time I would not consider purchasing. If it has control boards in it that may be the problem. You could be looking at hundreds of dollars to repair the unit.

  6. Sergio Spataro September 26, 2013 at 10:56 am #

    Hi, I have 2 fairly new pizza ovens (stacked) that keep blowing out.

    When I initially turn the oven on, it heats to temperature and unless I leave the door open (not the oven door, but the door to see under the stone, where the pilot light is) after a while it blows out the pilot light. Leading to the oven cooling down, right in the middle of a dinner rush.

    What is happening?

    Anyones help would be appreciated.

    • Tundra Restaurant Supply September 26, 2013 at 12:29 pm #


      It sounds like a draft problem is blowing out the pilot light. Do you mind sharing your make, model, and serial number, and we can dig into it a bit more for you?

      • Sergio Spataro September 26, 2013 at 1:42 pm #

        Make – Bakers Pride
        Model – D125
        Serial – F08A102

        On Both ovens we have to slightly open the “burner” door, in order for the pilot to not blow out when idoling. Sometimes, if the door isnt open enough it still gives out.

        Forgive me if my termonogoly isnt correct, as my borhter has been dealing with this more. But I believe we have changed the pilot light, thermopile and thermocupler, a few times. Seems to puzzle many ppl that we have had come look at the ovens.

        • Tundra Restaurant Supply September 27, 2013 at 1:38 pm #

          Our only thoughts would be that it could be the pilot safety valve, since it seems that you’ve already addressed other common issues. However, before continuing, we’d highly recommend contacting Baker’s Pride technical support to see if they can walk you through the repair. Their number is 800-431-2745. Good luck!

  7. Walter December 2, 2013 at 2:52 pm #

    I have a us range and the pilot will not light. I’ve rebuilt the safety valve and put in a thermalcoupler but still no light.
    I’m out of answers.

    • Tundra Restaurant Supply December 11, 2013 at 9:00 am #

      Walter, what type of unit do you have have? Fryer? Range? If it is a fryer, you might have a bad hi-limit. Try resting it, or jumper it out & bypass it if it’s bad.

  8. nick January 10, 2014 at 10:36 am #

    I have a blodgett 1060 double stack oven.i just replaced the pilot and thermocouple and the pilot will stay lit and the burners will fire up but for some reason the pilot just goes out.some times it will go for about an hr other times it runs for 20 min then shuts down.any ideas how to fix this?is there a way to get more flame on the pilot?

    • Tundra Restaurant Supply January 13, 2014 at 8:45 am #

      Nick, it sounds like a thermostat may be the issue. Try adjusting the regulator for more gas, and make sure the thermocouple is in the pilot flame too.

  9. Carb oven Repairs May 1, 2014 at 10:30 am #

    I have been working on these problems for 40 years so I know what’s going on You have no secondary air comming into that oven take out all the Bain burners and vacum that oven very good. Then replace the burners that will solve your problem as long as the safey valve is good This trick has worked for me so many times 718-288-4336

  10. Jennifer M August 21, 2014 at 12:01 am #

    We have an industrial Sunfire range it has griddle on top and 2 burners on right side. The oven is not working on this unit and I need it to work!! There’s no pilot lite for the oven. What do I need to fix it? Model # S-24G-2-26 I can’t seem to find the answer no matter what way I google it!! Please help!! Thank you!

  11. C.Smith December 20, 2014 at 12:58 am #

    I have a wolf c34s-4 old 1994 problem im having is the oven pilot lights and stays light until i actually turn on the oven, set to 250 or above works about a minute then both oven and pilot quit. wait 1 min or so relight and same thing ( safety valve issue?)

    • Kasy Allen January 12, 2015 at 3:52 pm #

      Sounds like a safety valve issue for sure, but you can have a local repair tech take a look to verify.

  12. SWilson March 11, 2015 at 8:36 pm #

    I have a Blodgett 1048 pizza deck oven that will not light. About a month ago I turned the thermostat up to heat the oven and the oven would not heat. I looked and the pilot light was lit, but the burners wouldn’t fire. I replaced the thermostat and the oven worked fine for about a month. Then one morning I tried to heat the oven up and it would not heat up. I checked the pilot and it was lit, however when I would turn the thermostat up the pilot light would go out. Id cut the thermostat back down and re-light the pilot and it would stay lit, but, once I turned the thermostat up the pilot light would go out I checked the location of the thermocouple tip an it was in the middle of the pilot flame as required. I’m not certain whether the symptoms I’ve described are indicative of a bad safety vale, a bad thermocoupling, or a defective thermostat. Like I mentioned the thermostat is new. The safety valve is a one way and does not have the thermocouple permanently attached. Any opinions would be greatly appreciated.

    • Chris Tavano March 16, 2015 at 11:21 am #

      I think you’re on the right track. It’s either the thermocouple or safety, but no way to really be sure. Blodgett’s tech support line may know of some tests you can do to check which part is bad before you purchase any more parts. Give them a call at 802-658-6600.

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