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NORMAL BURNER SEQUENCE OF OPERATION
1. APPLIANCE CALLS FOR HEAT BY RAISING THE THERMOSTAT TO THE DESIRED SETTING:.Note the transformer is
always energized with 110 volts.
2. When the thermostat circuit is complete, this allows 24 volts to coil side of the fan relay which are the bottom terminals.
3. Now that 24 volts (Yellow Wires)are applied to the coil, this in turn allows the 115 volt contacts to close thus allowing 115 volts
to flow to the fan across terminals #1 and #3 which are in series with the fan motor.
4. The Combustion fan motor should now be operational.
5. With the fan energized, there will be a 30 second pre-purge.
6. The Fan motor will develop 3400 rpm quickly causing the centrifugal endswitch to close. The End switch can be identified by
the two red wires coming from the end cap.
7. After the Endswitch makes, this allows 24 volts to the Honeywell S87K control
8. Now the Ignition process will follow.
9. The S87K will generate a high frequency spark at the same time the gas valve opens. The S87K has a 4 second trial for ignition
period; If after four seconds the control does not sense a minimum flame signal of .8 micoamps then the control will go into
lockout. To Reset the control simply cycle the thermostat off and then set it to the desired room temperature.
10. After the Burner is operational, the Honeywell control shifts into a rectification mode constantly monitoring the flame signal.
11. The Burner will now cycle off and on based on the thermostat setting.
COMPONENT SECTION
FAN RELAY MALFUNCTION
I . If the 24 volt coil fails to operate then the Fan Motor will not be energized. To check the coil for short circuit, power should
be off, set the multimeter setting to continuity. If the multimeter reads O.L then the 24 volt coil has break in its circuit and
must be replaced. Some multimeters have an audible Continuity setting. If the continuity thru the 24 volt coil is good then the
multimeter will beep and this part of the Relay is good. The Fan relay should have 24 volts across the lower coil terminals.
The 24 volts is supplied from the 24 volt transformer.
2. If 24 volts are present on the coil side but we do not have 115 volts on the contact side of the relay, then check the voltage
supply or look for a blown fuse. The 115 volts are supplied from LI (Hot) and L2(Neutral).The 115 volt contacts can be
checked easily by checking continuity also. Set multimeter to the continuity setting and place the black and red leads across
the terminals with the 24 volts on. If the multimeter does not make any sound then the contacts are open and the relay must
be replaced.
24 VOLT TRANSFORMER MALFUNCTION
1. The 24 volt transformer has a 115 volt primary side with a 24 volt secondary circuit. To check the transformer simply apply
115 volts to the black and white leads. If the transformer is working correctly, 24 volts will be present across the two yellow
leads. If the multimeter does not register 24 volts then the transformer needs to be replaced. The transformer will not function
unless 115 volts are present across L1 and neutral.
HONEYWELL GAS PRIMARY CONTROL
1. The Honeywell Primary Controls the burner operation. The Gas Primary requires 24 volts input into the control from the 24
volt transformer path. After the control receives 24 volts then the trial for ignition period begins. At this point we should have
24 volts into and out of the primary control. The Burner will have a 30 second prepurge followed by a 4 second trial for ignition
period. During the ignition process the control will be generating a spark at the same time the gas valve opens. After the flame
is established the flame signal strength should range from 2 to 5 micro amps and be stable. To check the flame signal strength
simply disconnect the black sensing lead from the Honeywell control and place the meter in series connecting one lead to
the black sensing lead and the other lead from the multimeter to the sensing post on the Honeywell Primary control.
HONEYWELL GAS VALVE MALFUNCTION
1. The gas valve is supplied with 24 volts from the gas primary which in turn is supplied with 24 volts from the 24 volt
transformer. During operation the two terminals on the gas valve should have 24 volts measured across the terminals. If the
24 volt transformer is working, the endswitch is made and the thermostat calls for heat but the gas valve does not open then
replace the gas valve.
