How Thermocouples Work on Ones Philadelphia Water Heater

Posted by on Dec 9, 2013 in Water Heater Repair Philadelphia | 0 comments

Ok, not to get too technical with you today, but Water Heater Repair Philadelphia wants to share some information on a water heater’s thermocouple.

The Family Handyman correctly concluded that “when thermocouples wear out, the pilot light goes out, the burner won’t light, and you don’t get any hot water.”

Standard style
Also called universal water heater thermocouple. It screws into below the gas valve and a probe on the other end slides into a holding bracket near the pilot light. It looks like a piece of copper wire.

Universal thermocouples are available in lengths from 15 to 36 inches. An 18 or 24 inch will be enough for all domestic water heaters utilizing universal kits. Nearly all older waters heaters and many of the newer design systems with a closed burner compartment and a seeing window will utilize this thermocouple.
If you wish to make use of an exact replacement length just eliminate your old one and measure it.

TCO design

Thermal Cut Off style has a re-settable thermal shut off switch indispensable into the thermocouple. In case of a flash fire or blow back from the burner the TOC will shut down gas flow to the burner and pilot. In case of a shut down the TOC needs to reset itself after it cools off and enable you to relight the pilot. The TOC switch looks like a watch battery. You will only find the TOC on newer design water heaters with seal burner compartments.

TOC non-resettable style

These thermocouples have a small TOC build inside the tube. They look just like a basic one other than the diameter is bigger about midways of television. When these TOC’s turn off they will not reset and should be replaced.

Exactly how Thermocouples Work

A pilot thermocouple sends a small electrical current to the gas valve when the probe is warmed to a specific temperature level. This electrical current informs the gas valve that the pilot is lit and its ok to send out gas to the burner if the thermostat requires it.  There are some great images to illustrate how this works here.

To test  a water heater thermocouple press the pilot button down on the water heater gas control valve. Then light the pilot. If after holding the pilot button down 30 to 60 seconds the pilot light goes out when you let go of the button, the thermocouple is most likely at fault on older devices. The TOC or air flow can be the trouble on newer systems with a pilot light viewing window.

If the pilot does not light at all the problem is gas flow, gas control valve, TOC tripped.

Usual Thermocouple Problems

The most usual trouble is the suggestion on the thermocouple probe weakens. It can quickly be replaced.

Thermocouple Repair

If the probe appears white in color this is carbon build up. It could keep the probe from getting hot enough to send a signal to the gas valve. Try sanding it with emery cloth and relight the pilot. It ought to work for a while however keep a brand-new thermocouple convenient.

  • The thermocouple probe need to be in the pilot light flame.
  • The thermocouple needs to be screwed into the gas valve firmly.
  • Check the pilot thermocouple tube for kinks.

Water Heater Repair Philadelphia hopes this has actually been an excellent intro to a water heater’s thermocouple for you!