What is the difference between a thermistor and a thermocouple?
A thermistor is a thermally sensitive resistor that exhibits a continuous, small, incremental change in resistance correlated to temperature variations. Thermocouples reflect proportional changes in temperature through the varying voltage created between two dissimilar metals electrically bonded together.
How do you measure a thermocouple?
The most common method is to measure the temperature at the reference junction with a direct-reading temperature sensor then apply this cold-junction temperature measurement to the voltage reading to determine the temperature measured by the thermocouple. This process is called cold-junction compensation (CJC).
What is inside a thermocouple?
A thermocouple is a sensor for measuring temperature. This sensor consists of two dissimilar metal wires, joined at one end, and connected to a thermocouple thermometer or other thermocouple-capable device at the other end.
Can a thermocouple be fixed?
The thermocouple is a safety device on a furnace. It has a metal rod that attaches to the furnace’s gas valve. If the thermocouple feels the heat from a pilot light, it keeps the gas line open. Luckily, cleaning or replacing a thermocouple is an easy fix that most handy homeowners can take on themselves.
What causes a thermocouple to go bad?
The presence of oxygen causes a reaction in the thermocouple that can wear down the part and make the wires become thinner and more brittle. Oxidation can be caused by a small amount of oxygen making its way into a sealed environment and reacting with the pure metal of the thermocouple.
How long should a thermocouple last?
one year
Why does my thermocouple keeps burning out?
It’s Dirty. Soot buildup on the thermocouple may block the flame. Under constant exposure to a hot flame, a thermocouple wears down over time. Even a slight residue can make the thermocouple malfunction.
Can you overheat a thermocouple?
If the back end of your thermocouple bulb gets constantly overheated, it will fail. With excessive back pressure coming from the burner ports, thermocouples can get burned up quickly.
Why does my pilot light keeps going out?
If the pilot light goes out, the thermocouple senses the drop in temperature and signals for the gas valve to close. If you have a faulty thermocouple is the most common reason that your pilot light is malfunctioning. Over time your water heater will collect dirt, dust and other kinds of debris.
How much does it cost to replace a thermocouple?
The thermocouple is an apparatus that senses whether the pilot light is lit and triggers the gas control valve. Repairs typically cost about $150 to have it done professionally, though a new thermocouple itself only costs about $20 on average.
What do I do if my pilot light keeps going out?
Pilot Light Instruction Guide:
- Turn off furnace, boiler, or water heater at thermostat or power switch.
- Locate the gas valve and turn knob from on or off (depending where it was) to pilot position.
- Hold down red button, which sends gas to the pilot burner.
- At the same time hold match to pilot burner.
Is it dangerous if the pilot light goes out?
Can a Pilot Light Outage Be Dangerous? The worry here is that when a pilot goes out, the gas valve that supplies the fuel for the pilot flame could still be pumping gas. This can mean a buildup of gas, and when the pilot is relit or relights itself it could result in a very serious explosion.
Can I relight the pilot light by myself?
Pilot lights were once standard on all gas furnaces, but newer systems don’t always contain pilot light ignition systems. Instead, some newer furnaces use electronic ignition systems. Often, homeowners can relight the pilot themselves.
Will gas shut off if pilot light goes out?
If the pilot light goes out on a storage or instantaneous hot water heater, space heater or a ducted heater, you will not have a gas leak. This is because all modern gas appliances with pilot lights have a fail-safe device that closes off the gas to the appliance in the case when the pilot may go out.
Does gas turn off when pilot goes out?
The pilot light is a small gas flame that stays lit all the time. When the thermocouple senses a lit pilot, it leaves the main gas valve open. If the pilot light is out, or isn’t burning hot enough, it closes the valve, cutting off gas flow so it won’t build up inside your house.
Are pilot lights always on?
The pilot light can be a “steady-on” pilot, or an ‘intermittent” or an electronic ignition system. The later type of pilot light is only on when the valve is open and the fireplace is operating. A millivolt valve utilizes a pilot light that is always lit.
Can you get carbon monoxide poisoning from a pilot light?
And a pilot light out of adjustment can produce carbon monoxide gas. The amount produced by even a badly maladjusted pilot is small because the flame size is also small. But in a small space without much air exchange, levels of CO could potentially build up to dangerous levels.
What thermocouple do I need?
Universal thermocouples come in lengths from 15 to 36 inches. An 18 or 24 inch will suffice for all residential water heaters using universal kits. Almost all older waters heaters and many of the newer style units with a sealed burner compartment and a viewing window will use this thermocouple.
What are the sources of errors in a thermocouple reading?
Six Common Causes for Thermocouple Temperature Measurement Errors
- Selecting the Wrong Type of Thermocouple on the Transmitter.
- Problems Related to the Thermocouple Extension Wire.
- Inherent Variations in Alloys.
- Temperature Variations Around the Reference Junction Connection.
- Thermocouple Grounded at More Than One Location.
What kinds of problems can be encountered in thermocouple use?
Common Thermocouples Application Problems and their Remedies
| Thermocouple Problem | Possible Cause(s) | Possible Remedies |
|---|---|---|
| Temperature indicating instrument shows room temperature | Thermocouple Lead wire break | Check continuity |
| Negative temperature indication | Incorrect polarity at Thermocouple | Reverse Thermocouple polarity |
How many types of thermocouples are there?
four different classifications
How much of a thermocouple should be in the flame?
A proper pilot flame should be blue with a yellow tip and should be strong enough to cover about 1/2 inch at the end of the thermocouple tip. If the flame is too strong and improperly adjusted, it will be blue but may be noisy and lift off the thermocouple, causing improper furnace operation.