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3. Total Shutdown.
A. When the high limit trips, 0.0 millivolts
will read across both coils of the
combination valve, causing both valves
to close.
B. Pilot relight cannot be accomplished until
oil cools sufficiently to allow high limit to
close.
C. If any wire in the system is cut or broken,
the system will shut down.
SYSTEM CONDITION QUICK CHECK
PROCEDURES
1. Use the Pilot Lighting procedure and check
millivolts (mV) at wires 3 and 4.
A. If the pilot lights, then pilot combination
and high limit are good.
B. If the pilot will not stay lit, check high
limit and open the thermopile circuit. It
should read 300 mV; if there are Ø volts,
check high limit. If the high limit is good,
replace combination valve.
C. Check for voltage at disconnected
thermopile. It should read 300 mV; if
there are Ø volts, replace thermopile.
Check high limit. If the high limit is good,
replace combination valve.
2. Turn on thermostat; burners should light.
A. If the burner does not light, check the
following:
1) Voltage at combination valve at
wires 2 and 4.
2) If correct voltage is present, then
check combination valve.
3) If there are Ø volts, check voltage
between wire 3 of combination
valve and wire 1 of thermostat. If
correct voltage is present, then
check resistance of thermostat
and wire 32. If there is no voltage,
check resistance of wire 1 to
normally open contacts of high
limit.
CONTROL SYSTEM DESCRIPTION
1. The thermopile (TP) provides the total control
voltage for this system.
A. One side of the thermopile is connected
to the common (C) of the high limit (HL).
B. The other side of the thermopile is
connected to the normally open (NO)
contacts of the high limit.
C. The common of the high limit (below the
high limit trip temp.) is connected through
the normally closed (NC) contacts of the
high limit, through wire 3 to the
combination valve pilot connection
common.
D. The other side of the pilot valve is
connected through wire 4 to wire 1 to the
high limit normally open contacts which
hold the pilot valve open.
1) If the high limit trips, connection is
made from the common to the
normally open contacts, turning off
pilot valve voltage. The gas valve
closes.
2. Thermostat Control.
A. One side of the millivolt supply is
connected through the high limit system,
as described above, to the thermostat
common (wire 3) of the combination valve.
B. The other side of the thermopile is
connected from the normally open
contacts of the high limit to the thermostat
through wire 1.
C. When the thermostat calls for heat (closed
circuit) power from the thermopile is then
connected to the other combination valve
thermostat connection through wire 2.
D. If the high limit trips, the thermopile is
connected across zero ohms, the output
voltage of the thermopile drops to 0.0
millivolts, and the thermostat coil of the
combination valve drops out, shutting
the thermostat valve.
ELECTRICAL OPERATION