Bradford White PDX-75S-70FB-3X - Manual (Page 26)

PDX SERVICE PROCEDURE VI
Gas Control/Thermal Well Testing and
Replacement
PDX Series
Thermal Well Testing
Thermal well testing
Position gas control power switch to
the “OFF” position and disconnect
thermal well harness from gas
control.
N
Y
Using a multi-meter set to the ohms setting, insert one meter probe (see caution)
into center wire position of thermal well connector, insert the second probe (see
caution) into either of the outside wire positions (see photo 20).
Alternate the probe on the outside position to the opposite outside wire position
(see photo 21).
Replace thermal well
(see page 27)
Using a multi-meter set to the
Ohms setting, determine the
resistance of thermal well sensor
(see caution photos 20 & 21)
Disconnect thermal
well wire harness
20 21
Replace gas control
(see page 27)
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Gas Control Testing
See pages 27 & 28 for gas control
input & output testing.
Once the thermal well resistance values are known, the water
temperature must also be known to determine if the resistance
values are correct. See page 25 to obtain water temperature.
Are thermal well resistance values correct?
CAUTION
DO NOT use standard multimeter probes for this test. Doing
so will damage connector. Use special pin type electronic
probes or small diameter wire pins inserted into connector.
If Control has gone into TCO lockout due to excessive
tank temperature (four flash, 3 second pause) reset
control by rotating knob of temperature control to the
minimum setting for at least 6 seconds before returning
to desired temperature setting.
Observe heater operation. If control
continues to lockout due to excessive
tank temperature, proceed to thermal
well testing to determine cause.
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