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Figure 1 

SEE THE APPLIANCE MANUFACTURER’S INSTRUCTIONS FOR THE SPECIFIC LOCATION.   

IF THE APPLIANCE MANUFACTURER DOES NOT SPECIFY A LOCATION, REFER TO FIGURE 1.   

BLOCKED VENT SWITCH   

WARNING:

  Read the installation instructions carefully and completely before proceeding with the installation.  

 

WARNING:

  Do NOT reset the device or restart the appliance unless the cause has been identified and corrected by 

a qualified agency. Insure the switch appliance combination has been cleaned by a qualified agency before placing 
back into service. Annual inspection and cleaning by a qualified agency is required. 

• 

Wiring 

MUST

 be in accordance with the current 

Canadian Electric Code

 and any other applicable federal, 

provincial and local code requirements. 

• 

For installations in the USA, all wiring shall be in accordance with the 

National Electrical Code

 and applicable local 

codes. 

• 

For continued safe operation, the appliance-switch combination is required to be inspected and maintained annually 

by a qualified agency.  Failure to properly maintain the appliance-switch combination can lead to Death, Personal 
Injury and or Property Damage. 

INSTALLATION 

M

OUNTING IN THE VENT PIPE

 

1.  Drill or pierce a clean hole (about 3/4” diameter) in the vent pipe near the appliance outlet. (See Figure 1) 

2.  The heat transfer tube must have the fiber gasket installed against the mounting plate before attaching the unit to the 

vent pipe 

3.  Insert the heat transfer tube with gasket into the 3/4” diameter hole placed in the vent pipe during step 1. 

4.  Secure the assembly to the vent pipe with a minimum of 4 sheet metal screws. The channel must be mounted 

horizontally, unless specified differently by the appliance manufacturer. (See Figure 1) 

CAUTION:

 

Disconnect electrical power supply to the appliance when wiring the blocked vent switch.

Model: WMO-1

 

The WMO-1 Blocked Vent Switch is
recommended for installation with an
oil fired appliance that normally
operates with its vent system under a
negative pressure. This device is
intended to detect a blocked vent
system, responds to hot flue gases
backing up through its heat transfer
tube, and can be wired to shut off the
oil burner. It requires manual resetting. 

This device MUST be installed by a qualified agency* in accordance with the manufacturer’s installation instructions. 

The definition of a qualified agency is:  

any individual, firm, corporation or company which either in person or through a 

representative is engaged in, and is responsible for, the installation and operation of oil appliances, who is experienced 
in such work, familiar with all the precautions required, and has complied with all the requirements of the authority 
having jurisdiction.

 

 

WARNING: 

Switch connection 
channel must be 
mounted horizontally, 
unless specified 
differently by the 
appliance manufacturer. 

I

TEMS SUPPLIED IN THIS KIT

1-Blocked vent switch assembly
1-Gasket 
1-Instruction sheet 

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