MILLIVOLT CHECK
(FOR QUALIFIED SERVICE TECHNICIANS
ONLY
)
The millivolt valve is a thermopile self-powered combination gas control. Before checking the millivolt system, the following
operations should be performed and observations made:
1. A genuine Keating millivolt thermostat should be used for millivolt operation.
2. The thermostat leads and all wire connections should be cleaned and tightened to eliminate all unnecessary resistance.
3. If pilot will not remain lit when gas valve knob is released, check automatic pilot.
NOTE:
The millivolt system and individual components may be checked with a millivolt meter having a 1-1000MV range.
Conduct each check below by connecting meter test leads to terminals as indicated. All readings are closed circuit.
A. BURNER COIL CHECK
(“A” Reading. Thermostat contacts CLOSED - Gas Valve knob “ON”. Main burner should come ON.)
1. If the reading is more than 100 millivolts and the automatic valve still does not come one, replace the valve.
2. If the closed circuit reading (“A” reading) is less than 100 millivolts, determine cause for low reading and proceed as follows:
CHECK
TO TEST
CONNECT METER LEADS TO
TERMINALS
THERMOSTAT
CONTACTS
METER READING
SHOULD BE:
A
BURNER COIL
TP
TH
CLOSED
100mV OR MORE
B
THERMOPILE OUTPUT
THTP
TP
OPEN
BETWEEN 325–700mV
C
THERMOSTAT LOAD
THTP
TH
CLOSED
DROPS LESS THAN 80mV
D
AUTOMATIC PILOT DROPOUT
THTP
TP
OPEN
BETWEEN 75-25 mV
THERMOSTAT BULB PLACEMENT DETAIL
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