John Wood Envirosense Power Direct Vent (May 2010 or later) - Manuel (Page 13)

13
CONTROLS AND SWITCHES
This model is provided with three pressure switches. These switches
are essential to the safe and proper operation of the unit. All switches
are wired in series. The controller is set up to shut the unit down
whenever there is a failure of any of the switches. It is important to
understand the purpose of each switch.
50 GALLON UNIT
75 GALLON UNIT
Figure: 2
BLOWER PROVER SWITCH
The Blower Prover Switch is provided on the heater to verify that
the fan is operating. It is a positive pressure switch whose electrical
contacts are normally open. When the fan increases the pressure in
the burner, the pressure switch will allow the electrical contacts to
close. The pressure switch is connected to the blower pressure tap
by a piece of tygon tubing. This tubing must be connected in order for
the switch to change the electrical contacts. The controller requires
that the electrical contacts on this air flow switch be open before it will
allow the blower to come on.
BLOCKED EXHAUST SWITCH
The Blocked Exhaust Switch is set up to shut the unit off when a build-
up of positive pressure in the exhaust vent pipe occurs. This switch
is a positive pressure switch that requires an increase in pressure to
change the electrical contacts from normally closed to open. When
this switch prevents the unit from igniting, most likely the exhaust is
blocked by some means. Check to see if the condensate is allowed
to flow freely from the exhaust elbow and for obstructions in the
exhaust venting and exhaust vent terminal. Also verify that the vent
length does not exceed the maximum allowed as shown in the Vent
Section of this manual.
BLOCKED INTAKE SWITCH
The Blocked Intake Switch is set up to shut the unit off when a
build-up of negative pressure in the intake air pipe occurs. This
switch is a negative pressure switch that requires an increase
in negative pressure to change the electrical contacts from
normally closed to open. The switch is connected to the pressure
tap on the PVC pipe connected to the inlet of the blower. When
this switch prevents the unit from igniting, most likely the intake
is blocked. Verify that the screen on the intake air connection
(conventional vent), the intake air pipe and termination (direct
vent installations) are free of obstructions that may prevent air
from entering the unit. Insure the screen on intake air connection
has been removed on direct vent installations, see “Figure 13:
AIR INTAKE SCREEN”. Also verify the intake air pipe length
does not exceed the maximum allowed as shown in the Vent
Section of this manual.
WATER HEATING ENABLE/DISABLE (ON/OFF) SWITCH
The Water Heating Enable/Disable (On/Off) Switch is a single-pole,
single-throw rocker switch. This switch provides 24V power to the
gas control valve.
SPARK IGNITER
The Spark Igniter is a device that ignites the main burner by spark.
When high voltage is applied to the igniter, spark is generated to
ignite the main burner.
Blocked
Intake
Switch
Blower
Prover
Switch
Blocked Exhaust
Switch
Blower
Prover
Switch
Blocked
Intake
Switch