Troubleshooting continued
Pilot does not stay lit —
Troubleshooting thermocouple or thermopile and high limit control circuit
1.Checking thermocouple or thermopile open system (Figure 10):
a.Use an electronic multimeter, with leads fitted with alligator clips. Set meter scale to DC Millivolts.
b.Unscrew thermocouple or thermopile fitting from gas valve.
c.Attach one meter lead to the end of the thermocouple or thermopile gas valve fitting.
d.Attach other meter lead to thermocouple or thermopile lead (copper sur- face).
e.Follow Lighting Instruction label on boiler (also found in Control Supple- ment or User’s Information Manual) to light the pilot burner only, and hold the pilot flame manually. (DO NOT light main burner.)
f.Check the reading on the multimeter. The reading should be around 28 millivolts for a thermocouple, or 700 millivolts for a thermopile.
g.If multimeter reading is significantly less than above and pilot flame is appropriate, replace the thermocouple or thermopile.
2.Checking thermopile and high limit control circuit closed system (Fig- ure 11):
a.Use an electronic multimeter, with leads fitted with alligator clips. Set meter scale to DC Millivolts.
b.Loosen the insulated terminal on the TOP thermopile lead wire enough to allow clipping a multimeter alligator clip to the spade terminal.
c.Attach the other multimeter lead to the thermopile lead (copper surface). Light the pilot burner per step 1 e, above.
d.Check the reading on the multimeter. The reading should be around 400 millivolts.
e.If reading is significantly less than 400 millivolts, check tightness of lead wire assembly in gas valve. If the connections are secure and you have checked the thermopile per step 1 above, replace the thermopile lead wire assembly.
f.If reading on TOP thermopile lead wire is around 400 millivolts, move the multimeter alligator clip to the BOTTOM thermopile lead wire terminal and check multimeter reading.
g.If multimeter does not read around 400 millivolts, check wiring connections and wire integrity to the high limit control.
h.Check voltage at each limit terminal to make sure limit is closed. Correct pressure or temperature condition causing any limit to be open. Replace limit if necessary.
Figure 10
Figure 11
20 | Part Number |
