Check Exhaust Tube Pressure
Blocked Vent Pressure Switch Testing and
Replacement for serial number “CF” and later
Exhaust Tube
pressure tap location
Exhaust tube
at bottom of heater
N
Replace
blocked vent switch.
(see “Blocked Vent
Switch Testing and
Replacement”)
Is exhaust venting
system blocked or
obstructed? Also
check condensate
elbow and drain.
Clear obstruction.
Determine cause
and correct.
Y
Is vent system total
length compliant with
vent tables in the
instruction manual?
Reconfigure vent
system to be
compliant with
vent tables (see
“Specifications”).
Y
N
With monometer, take a
reading at the exhaust
tube pressure tap location.
Is value negative (-) or
slightly postitive
(see illustration below).
Y
N
With ohmmeter check
pressure switch for
continuity. Contacts should
be closed.
Y
N
Pressure switch O.K.
58
Is pressure in exhaust tube near 2.7" w.c. or more? If so, correct
blockage (above). If exhaust pressure is low (0.40" or less),
replace pressure switch.
58