How to test water heater thermocouple

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How to test water heater thermocouple

When two wires made of different metals are joined and one of the ends is heated, there
is continuous current which flows in the thermoelectric circuit.
Test thermocouple/ pdf
Test thermocouple and thermopile/ pdf
Full service manual/ pdf

1) Check if gas is getting to pilot light. If gas is getting to pilot light and there is ignition, then water heater ECO is not tripped.
2) Check if pilot flame is weak or yellowish, then clean burner parts and air intake, and check gas pressure.
3) Get more air to water heater and check pilot flame again.
How to troubleshoot pilot light going out

Thermocouple: Initial test
1) Light pilot. Hold down pilot button for 30 to 60 seconds.
2) Relase pilot button.
4) If pilot light goes out when button is released, then thermocouple is most likely at fault.
Resources for replacing thermocouple

With the pilot flame lit, turn OFF the gas supply and start to
count seconds (one-one thousand, two-one thousand). Count
for a full twenty (20) seconds. The pilot flame should be out.
Listen carefully for a small clicking noise at the gas inlet side
of the valve. If you count for the full twenty (20) seconds and
do not hear a click then the thermocouple is fine.
If you hear a click within the twenty (20) seconds then the
thermocouple and or gas valve is bad. Replace both the
thermocouple and gas valve.

If you can get PILOT or MAIN BURNER – even for a couple of seconds, then the ECO if good. Otherwise replace gas control valve.

End of thermocouple must be embedded in pilot flame

If pilot light stays on without problems as long as gas valve is in PILOT position, but you then turn to ON position and main burner flutters and disappears within 30 seconds then 99% chance TRD is tripped.' Read about TRD/ FVIR

Larger image

Typical gas control thermostat with thermocouple:

If gas water heater has standing pilot light, then copper tube will be connected to the gas valve.

Thermocouple cannot have kinks, but copper can be rolled if thermocouple is too long.
Thermocouple is finger-tight plus 1/4 turn.
Overtigntening thermocouple will short electrical signal to gas control valve.

Test thermocouple with multimeter

Remove thermocouple from gas valve using 7/16" wrench.
Thermocouple is finger tight + 1/4 turn
Some thermocouples are reverse threaded.
Instructions for testing thermocouple:
Thermocouple has 2 ends: one end screws into gas valve, other end is positioned in the pilot flame.
1) Make sure thermocouple is positioned correctly in pilot flame.
2) Disconnect thermocouple from the gas valve thermostat using 7/16” wrench.

3) Using multimeter with alligator clip leads:
Attach red lead to the body (copper part) of the thermocouple.
Attach black lead to the end (silver part) of the thermocouple that connects to thermostat.
4) Follow instruction to light the pilot and watch voltage readings on multimeter.
5) If thermocouple is good, then after 45 seconds the meter should read 12 millivolts or more.
6) Clean end of thermocouple and clean inside gas valve connection before reattaching thermocouple.

Typical multimeter might not have alligator clips.

Without alligator clips you may need extra hand to keep pilot flame lit during test.

Things to remember about thermocouple Finger tight + 1/4 turn
	1) CLEAR BLUE FLAME: Pilot Flame and Burner Flame must be clear blue color. Other colors such as orange and yellow indicate that burner parts, pilot orifice, and combustion chamber need to be cleaned. More resources 2) Water heater needs oxygen for combustion. If pilot is going out, then clean air intake and get more fresh air to water heater to see if problem is solved. 3) Thermocouple must sit in the pilot flame so it will stay hot. Heated thermocouple sends small electric current to gas control valve. If gas control is defective, or thermocouple is bad, or pilot blows out, or pilot flame is weak, or thermocouple has fallen loose, then gas control valve turns off pilot. 4) Re-install thermocouple: finger tight + 1/4 turn. If thermocouple is too tight, the insulator is crushed and the thermocouple shorts out against the gas valve. The gas valve cannot read the current and shuts gas off to pilot. Read step to replace themocouple More resources: How to replace thermocouple/ Utube How to replace thermcouple 2/ Utube How to replace thermocouple pdf Burner is sometimes removed to replace thermocouple. In that event, go ahead and clean combustion parts and combustion chamber. If LP gas is used, then manifold tube has reverse threads. Be careful of reversed threads. When re-attaching burner tubes to gas control, use fingers to start the threads. Always check pilot and manifold tubes for gas leak using soapy water. Clean combustion parts and troubleshoot gas water heater

Honeywell Icon gas control:
Gas control monitors Thermostat Temperature sensor. When setpoint temperature is satisfied, the gas control is shut down, and power removed from relay. The gas control LED flashes steady flash each 4 seconds.
If flame is lost, the pilot and main valves are shut down. The gas control attempts to re-light the pilot 4 times. If unsuccessful, then power is removed from relay, and the gas control proceeds to a 5 minute lockout. The gas control re-attempts to light the pilot at next normal heating sequence.

Pilot assembly is replaced on this type of gas valve.
Service manuals at Bradford White
Service manual for the Honeywell Gas Control Valve
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All Costs are energy, so total energy-cost equals cost of water heater, plus installation, plus expected repairs-and-parts, plus water softener-and-filter, plus disposal-recycling cost, divided by years of tank life. These numbers are added to monthy energy cost to measure true energy cost & efficiency of a water heater.
Government/industry efficiency numbers consider only energy cost per gallon of heated water.

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