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Archive | December, 2009

Fixing Commercial Ovens: Pilot Light Won’t Stay Lit

80% of the time the thermocouple causes this problem.  When lighting the pilot, if the thermocouple is not directly in the flame it doesn’t get hot enough to allow it to open the safety valve.  If it is directly in the flame and it won’t stay lit then the thermocouple is probably defective and needs to be replaced,  Keep in mind that some safety valves have the thermocouple permanently attached so the entire valve must be replaced. Fixing Commercial Ovens: Pilot Light Wont Stay Lit

If you’ve replaced the thermocouple and attempt to light the pilot and it still will not stay lit then the safety valve is defective.  Remember to check the type of safety valve you have to get the correct replacement.  For correct identification  procedures check out this Tech Talk post.

When working on any type of gas equipment always remember to shut off the gas!

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Replacing Top Burner Gas Valves On A Commercial Range

Top burner gas valves are fairly easy to replace.  With the top plate (bull nose) removed you can access them easily (part of the frame runs across the top of them).  If you are replacing all or just one, the burners must be removed if they have a slip type orifice.  If there is a tube type burner valve they need not be removed because you can disconnect the tube from the burner valve and move it out of the way.  Replacing Top Burner Gas Valves On A Commercial Range

In either case when the burners or the tube is disconnected take a wrench and screw out the valve being replaced (in some cases you may have to remove a pilot adjustment valve to be able to turn the burner valve by it).

Once the old valve is removed, put some gas thread sealer on the treads of the new valve and screw it back into position, being careful not to over tighten.  Reassemble the unit except for the top plate.  Turn the gas back on and light the pilots (this may take a few minutes because the gas must first force out the air in the manifold).

Once the pilots are lit, turn on the first burner.  There may be no gas flow because the orifice on the new valve may be closed.  Using two wrenches, one to hold the valve the other to turn the orifice, open the orifice to allow gas flow (this may take a couple of turns).

Once the burner lights, continue to adjust the orifice until there is a nice blue flame.  Adjust until you have as little of a yellow flame as possible. If you feel there is still too much yellow flame you may need to adjust the air shutter located on the end of the venturi.  Once you have produced the bluest flame you can get, you are done.  You can reassemble your range and cook to your heart’s content.

Make sure you have the right orifice for the type of gas you are using!  Natural gas and LP gas require a different sized orifice.  If you are having problems with the flame on the burner, check the number on the orifice.  The larger the number, the smaller the hole.  Large number orifices are for LP gas.  Smaller numbers are for natural gas.

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Replacing Commercial Range Top Burner Pilots

Top burner pilots need to be replaced if they become clogged.  They are very difficult to unclog, and generally need to be replaced. There are three types of pilots:

  1. Those with the tube pre-welded to the pilot head.
  2. Those that have a nut and ferral to slide over the tube and be tightened onto the tube.
  3. Pre-formed pilot assemblies specific to a particular range.  Replacing Commercial Range Top Burner Pilots

Finally, there are new “flex tube” pilot burners that have a flexible pilot tube, making them very easy to install.

When replacing the pilots you will have to remove the front top plate (bull nose) from the range to access the pilot adjustment valves.  This will also have to be removed to replace the burner valve described below.

The pre-welded type is fairly easy to install.  To replace, disconnect the pilot tube from the pilot adjustment valve and remove.  Place the new pilot head and tube next to an existing one and follow the contour while slowly bending to form the same shape.  When you get to the end you may need to cut the tube off, using a tubing cutter.  A nut then needs to be put on, and then a ferral and screw back onto the pilot adjustment valve.

The type with the nut and ferral is very easy.  Simply use a tubing cutter and cut if off just below the old pilot head.  Remove the nut and ferral from the new replacement pilot head and slide them over the tube, nut first and then the ferral.  Slide the pilot head onto the tube and tighten the nut up to the pilot head.

The pre-formed pilot assemblies are far easier because they are all bent and ready for installation, the only draw back is they are a little more expensive than the others.

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Replacing Commercial Range Burner Heads

Burner heads usually become plugged over time.  There are two screws that connect the head to the venturi.  It is a good idea to use some kind of rust dissolver on the screws to loosen them.  Once the screws are out you can install the new head, and always remember to replace the gasket as well.

Some burner heads, most notably Southbend, are one piece and do not have a separate venturi.  In these cases the whole piece needs to be replaced.

One alternative to replacing the head is to get a drill bit the same size as the holes in the head and drill out the grease build up in them.  However, this can sometimes alter the flame pattern.

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Replacing Burner Grates For Commercial Gas Ranges

The top burner grates only need replacing if they have cracked due to metal fatigue or if they have been dropped and broken.  To replace, simply pull the broken grate off the top of the range and then place the new grate over the burner.

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