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Tundra’s Tech Talk helps you learn how to fix you restaurant & food service equipment on your own – DIY. Ask one of our experienced technicians a question, or learn about other equipment we’ve already helped other readers with.

Fixing Commercial Oven Problems


Oven problems are fairly simple to diagnose.

The most common complaints are:

  • The pilot won’t stay lit.
  • The oven won’t get up to temperature.
  • The oven gets too hot.
  • The oven does not cook evenly.

ThermocoupleProblem number one is probably the most common.  Usually it’s the thermocouple that causes this problem.  When lighting the pilot, if the thermocouple is not directly in the flame it can not 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.

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!

Number two is usually a thermostat problem.  When you set the thermostat at a set temperature and it does not reach that point it may be one of two problems:Gas Thermostat

1. The thermostat may be defective.
2. The thermostat may be out of calibration.  To check the calibration get a thermometer that you know is accurate.  Put it in the oven and set the thermostat to 250º.  Open the kick plate below the oven door and watch the burner flame, if it goes off before the oven reaches 250º you may be able to calibrate it.

To calibrate a thermostat remove the knob and check to see what type of thermostat you have.  The thermostat is either a type with a round disk that has two screws holding it in place or it will have a D shaft with a small screw in the center of it.  In either case only turn the disc or screw a fraction of a turn at a time and no more than a quarter turn either direction.

Continue to turn the disc or screw a fraction of a turn each time until you see the burner come back on.   If you reach that quarter of a turn point and the burner does not come back on, the thermostat is defective and must be replaced.  If the burner comes back on, watch the temperature of the oven and if it gets to within 5 or 10° of the preset temperature, you are good to go.  It may take several tries to get it properly calibrated.

If you still can not get it calibrated within the temperature range, you need to replace the thermostat.  All thermostats are preset from the factory and should not require calibration when installed.  If you find that the new thermostat does require calibrating, follow the previous instructions.

Number three is also a thermostat problem.  Follow the same procedure to calibrate as you did for the oven not getting to temperature.  Again, if you can’t get it to calibrate, replace it and the oven should heat to the correct temperature.

Number four is a common problem after a new thermostat has been installed.  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.

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.

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Identifying Electric Cooking Equipment Elements

There are five types of elements in electric food service equipment:

1. Calrod (metal) type
2. Glass tube (quartz) type
3. Ceramic type
4. Wire type
5. Solid typeReplacement Electric Elements

These five elements are either submersible, dry, or both.  No matter what type of element you’re trying to replace, the most important piece of information you need is the element’s manufacturer, model, and serial number.  Search for elements by manufacturer here.

When working on any piece of equipment always remember to disconnect the POWER!

Calrod elements are found in both overhead warmers and well type warmers.  The well type warmer can be a counter top or a steam table warmer.  The configuration (shape) of the elements depends on which unit they go in.  Most overhead warmers use a straight calrod or glass tube element.  Steam table elements can be many different shapes: u-bend, w-shape, s-shape, round, etc., so the best means of identification is by brand name, model and serial number.  The voltage is also very important.

Glass tube type elements have a wire element curled like a spring inside a glass tube. These elements are found in overhead warmers, cheesemelters, and some conveyor type toasters and impingers.  The best way to identify these elements is with brand name, model and serial numbers as well as voltage.

Ceramic elements are most commonly found in overhead warmers.  Although they are a rarity, the same identification method should be used, model number, serial number and voltage.

Wire type elements are usually those that are referred to as a card element.  This means the element is a thin flat wire or spring type wire that is wrapped around some type of conductive flat card.  This type of element is most commonly found in pop up or pop down toasters.  For proper identification, again having the model and serial number and the voltage is very helpful.

Solid type elements are calrod or filament elements and are incased in a block of metal or possibly ceramic.  They come in various sizes and shapes but perform just like other elements.  They can be found in warmers, toasters and even chafing dishes.  The best way to identify these elements is by brand name, model and serial number and voltage.

If you can’t find a brand name, model or serial number, there is another way to identify that element (and this goes for all elements).  Every element has information either stamped into it or stenciled on to them.  You may need a magnifying glass to read the information (especially on calrod elements).

The information you need to find on the element is:

1. Voltage
2. Wattage
3. Part number
4. Color coding

With this information, it is more likely that you will receive the correct element the first time.  Also don’t forget the style and the piece of equipment it is in.  Remember, there are many pieces of equipment that have elements, and the above information also applies to their identification.

Check out more food service parts.

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Repairing Countertop Warmers

Countertop WarmersSummary – Countertop warmers keep pre-cooked foods warm.  In this Tech Talk, learn how to replace all 4 components that could fail in your countertop warmer.

Critical Note – Never run the warmer without water!

For best results, use the model and serial number on your warmer to identify the right part or call 1-888-388-6372 for help.

There are only four components that can fail in these units.

1. Thermostat (infinite control, bi-metal, or thermostat with capillary)
2. Element
3. Hi-limit
4. Indicator light

Failure of any of these parts with the exception of the indicator light will cause the unit to fail.

How do I repair my warmer?  Which part do I need?

If your warmer is not working at all, begin by unplugging the unit.  Remove the bottom panel and inspect the element for burn spots.  Look for burned wires and connectors.  If the wiring and element appear fine the next step would be to check the hi-limit switch.

This will require an electrical test instrument.  You can use either a simple continuity tester or a multi-tester.

Begin by disconnecting the wires from the hi-limit switch.  Set your tester on the continuity setting and put the leads from the tester on each side of the hi-limit.  If there is continuity (a constant beep from the tester) through the high limit, then it is good.  If there is no continuity the hi limit is bad and must be replaced.

Let’s discuss the thermostat.  You have one of three types.

1. Infinite control – These usually have five to six pins coming out of the back.  To test this control, use your electrical tester.  Set it on the continuity reading.  Make sure the infinite control is turned on!  Connect one lead to H1 the other to H2.  If there is no continuity reading between H1 and H2 then the control is bad and must be replaced.

2. Bi-metal – This is an open control and you can see the contact points inside of it.  Turn the stem to see if the points open and close.  If the points do not snap together, the control is bad and must be replaced.

3. Capillary type thermostat – The last thermostat is one that has a capillary tube with a bulb at the end (attached to the control).  Follow the same procedure for testing as you would for the infinite control.

4. Last is the indicator light. If the light burns out it will not effect the operation of the unit.  It is simply there to indicate if the unit is on or off.

You can also test the element with the electrical tester set for continuity.  Remove both wires from the element and put the leads from the tester across the element connections.  If continuity exists you will hear a continuous beep from the tester.  If there is no beep, the element is bad and must be replaced.

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Replace Commercial Refrigeration Thermostats Yourself

There are two types of temperature controls used in commercial refrigeration:

1. Thermostatic (either an air sensing type or evaporator coil sensing type)
2. Low pressure controlAn Air Sensing Refigeration Thermostat

Let’s start with thermostatic type controls.  An air-sensing thermostat does just that: it senses air temperature.  The control sensor tube is usually mounted in the evaporator housing.  The evaporator is located inside the unit, usually at the top where the fan motor is mounted.  The thermostat has a straight capillary or sensor.  The capillary tube is mounted on the outside of the evaporator coil usually pushed into a tube that is mounted in the front of the evaporator.

An Evaporator Coil Sensing ThermostatAn evaporator-sensing thermostat has a coiled capillary tube attached to it, which you can see pictured as a tight spiral to the left.  The evaporative sensing capillary or coiled tube end push into a hole that is in the evaporator.  It senses the temperature of the evaporator coil rather than air temperature.

These two controls are not interchangeable. If you put an air sensing control in place of an evaporative sensing control, the evaporator unit will shut off permanently, causing the temperature to rise.  If you put an evaporative sensing control in place of an air sensing control the unit will continue to run, causing the evaporator to freeze up.  If this happens there will be very little airflow, causing the temperature to rise.

How to spot a defective thermostat:

A commercial refrigeration thermostat can fail in two ways: in an open position or a closed position.

If the thermostat fails in the open position, the unit will not run at all.  To check this, remove the screws from the evaporator housing (make sure the unit is unplugged or the breaker is off) and pull the housing down.  Locate the wires attached to the thermostat and remove them.  Connect the two wires together and tape with electrical tape.  Turn on the breaker or plug the unit back in.  If the unit runs, replace the thermostat.

If the thermostat fails in the closed position, the unit will run all the time.  Running constantly will cause the evaporator to freeze up, restricting the airflow and causing the temperature to rise.  Use the same procedure described above to test the unit and replace the thermostat if necessary.  Also be sure to defrost the evaporator before turning the unit back on.

If the evaporator continues to freeze up after the thermostat replacement, call a service company as you may have other problems requiring a trained technician.

The other type of control is a low-pressure control.  These are usually located in the compressor compartment.

A low-pressure control is connected into the refrigeration lines and controls the temperature by using the pressure of refrigerant flowing through the line.  This type of control requires a service technician to replace.

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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.

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Repairing Overhead Warmers

An Overhead WarmerOverhead warmers are fairly simple devices.  They are typically used to keep food that is ready to be served warm before it goes out on the server’s tray.  Overhead warmers have three main parts:

1. Element
2. On/off switch
3. Infinite Control

Warmers come in different voltages such as 120V, 208V, and 240V, and they are made in different lengths.  Always remember that it’s crucial to have the correct voltage on the unit, because severe damage can happen when the unit is introduced to the wrong voltage.  There are two types of elements in most overhead warmers.

1. Cal-rod (metal) type
2. Quartz glass type.

These elements vary in wattage and length.  When replacing an element, it is helpful to provide the following information to ensure you get the correct element.

1. Overall length of the warmer
2. Model Number
3. Serial number
4. Voltage

This information can be found on the name tag that is attached to the warmer.

There are two ways to determine if an element is bad:

1. Visual Inspection. On the Cal-rod element, inspect the outside for burn marks.  On the quartz element, inspect the filament or wire coil inside the glass tube.  If it is separated in any way, it is burnt out.A Nemco Overhead Warmer Element

2. Continuity Testing. A continuity tester can determine if an element is defective.  Remember to disconnect the power! For either element (cal-rod or quartz), first remove at least one wire connection or remove the element if it is a socket type.  If you have a Multi-Tester set your tester in the continuity position and touch the leads to the element.  If there is no digital read out on the display the element is no good.  If you’re using a lighted tester and the light does not light up, then the element is not good.  In either case, the element needs to be replaced.  The element is still good if you get a digital read out or the lights does light up.

A General Use Rocker On/Off SwitchOn/Off Switch

To test the on/off switch, disconnect at least one wire from the switch and perform a continuity test with the switch in the on position.  If you do not get a reading, then you need to replace the on/off switch.

Infinite Control

To test the infinite control, there are multiple wire connections on the back of the control.  These wire connections are marked as follows:  L1 and L2 are the power wires coming in the warmer.  H1 and H2 are the connections for the element wires.  On units with a pilot light there may be a HP connection or a P connection, P meaning pilot light connection.  A General Use Infinite Control

Disconnect at least one wire from any of the H connections and perform a continuity test across the H prongs with the control in the on position.  If you did not get a reading or light it is time to replace the infinite control.  On an infinite control make sure to determine if it is a  screw mount or nut mount before purchasing a replacement.  Screw mount controls screw into the overhead warming unit; nut mount controls bolt onto the unit.

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