ULTRAFORCE COMMERCIAL GAS WATER HEATER
SUF 120 thru 400 SERVICE HANDBOOK
State Water Heaters – Technical Traini ng Department 27 Ashland City, Tennessee © 2009
Servicing should onl y be performed by a Qualified Service Agent 198152-002
CONTROLS – PRESSURE SWITCHES – ALL MODELS

All SUF models are provided with four pressure

switches. These switches are essential to the

safe an d proper operation of the unit. The

switches are wired to the central control board

(CCB) individually and ea ch is monitored

individually. The (CCB) is set up to shut the unit

down whenever there is a failure of any of the

switches and declare a fault for each individual

switch. It is important to understand the purpose

of each switch.

BLOWER PROVING SWITCH
The Blower Proving Switch i s provided on t he
heater to v erify that th e fan is oper ating. It is a
positive pres sure switch whose electrical contacts
are normally open. The blower proving switch
electrical contacts will close on a rise in pressure
as the blower increa ses the pressure in the burner.
This sw itch is connecte d to the burner tap by a
piece of Tygon (soft plastic) tubing. This tubing
must be connecte d in order for the switch to clos e
the electrical contacts. The controller requires that
the electr ical contacts on this pressure switch be
open before it will allow the blower to come on. The
control will declare a fault on the U IM if either
condition occurs.
BLOCKED OUTLET PROVING SWITCH
The blocked outlet proving s witch electrical contacts
are normally closed. Th e blocked outlet pr oving
switch elec trical contacts will open on a rise in
pressure. Check t o see i f the c ondensate i s
allowed to flow freely from the exhaust elbow and
for obstructions in the exhaust venting and exhaust
vent term inal. Also check the that the equival ent
feet of vent pipe for the specific m odel has not been
exceeded. Check the vent leng th tables on page 9
BLOCKED INL ET PROVING SWITCH
The Blocked Inlet Prov ing switch electrical contacts
are normally closed. The blocked inlet proving
switch electr ical contac ts wi ll op en when an
increase in negativ e pressur e (vacuum ) occurs
in the intake v ent pipe. The switch is connecte d to
the pressure tap on the PVC flange connected to
the inlet of the blower. When this switch prevents
the unit f rom igniting, most likely the intake is
blocked by some means. Verify that the air intake
pipe and ai r intake v ent ter minal are f ree of
obstructions that may prevent air from entering the
unit. Also check the that the equivalent f eet of vent
pipe for the specific m odel has not been exceeded.
Check the vent length tables on page 9
LOW GAS PRESSURE SWITCH
The Low Gas Pressure Switch electrical contacts
are normally open. The low gas pressure switch
electrical c ontacts will close on a rise pres sure.
The contacts w ill open w hen the pressur e falls
below the fixed set point. If this happens during a
heating cycle a the burner will be shut down and a
fault will be declared on the UIM.
Low Gas Pressure
Switc h
Pressure
Switc hes