Thermal Well Testing - Bradford White M1TW40S Series Service Manual

Gas Control Testing
See pages 29 & 30 for gas control
voltage testing.

Thermal Well Testing

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.
Thermal well testing
Position gas control power switch to
the "OFF" position and disconnect
thermal well harness from gas
control.
Using a multi-meter set to the
Ohms setting, determine the
resistance of thermal well sensor
(see caution photos 19 & 20)
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?
Replace gas control
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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.
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 19).
Alternate the probe on the outside position to the opposite outside wire position
(see photo 20).
Y
(see page 26)
TTW SERVICE PROCEDURE VI
Gas Control/Thermal Well Testing and
Disconnect thermal
well wire harness
19
CAUTION
N
Replace thermal well
(see page 26)
Replacement
20
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