Specifications

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Servicing should only be performed by a Qualied Service Technician
CONTROLS – PRESSURE SWITCHES – ALL MODELS
All BTH models are provided with four pressure switches. These switches are essential to the safe and
proper operation of the unit. The switches are wired to the central control board (CCB) individually and
each 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.
Low Gas Pressure
Switch
Pressure
Switches
BLOWER PROVING SWITCH
The Blower Proving 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. The blower proving switch electrical contacts will close
on a rise in pressure as the blower increases the pressure in the burner. This switch is connected to the
burner tap by a piece of Tygon (soft plastic) tubing. This tubing must be connected in order for the switch to
close the electrical contacts. The controller requires that the electrical contacts on this pressure switch be
open before it will allow the blower to come on. The control will declare a fault on the UIM if either condition
occurs.
BLOCKED OUTLET PROVING SWITCH
The blocked outlet proving switch electrical contacts are normally closed. The blocked outlet proving switch
electrical contacts will open on a rise in pressure. If a fault occurs, 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 check that the equivalent feet of vent pipe for the specific model has not been exceeded. Check the vent
length tables on Page 11.
BLOCKED INLET PROVING SWITCH
The Blocked Inlet Proving switch electrical contacts are normally closed. The blocked inlet proving switch
electrical contacts will open when an increase in negative pressure (vacuum) occurs in the intake vent
pipe. The switch is connected to the pressure tap on the PVC flange connected to the inlet of the blower. If
the switch is open,, most likely the intake is blocked by some means. Verify that the air intake pipe and air
intake vent terminal are free of obstructions that may prevent air from entering the unit. Also check that the
equivalent feet of vent pipe for the specific model has not been exceeded. Check the vent length tables on
Page 11.
LOW GAS PRESSURE SWITCH
The Low Gas Pressure Switch electrical contacts are normally open. The low gas pressure switch electrical
contacts will close on a rise pressure. The contacts will open when the pressure falls below the fixed set
point. If this happens during a heating cycle the burner will be shut down and a fault will be declared on the
UIM. If a fault occurs, check gas line pressure with a manometer, adjust the gas supply line pressure "Gas
Pressure Specifications" table on Page 4.