COMET 145 – INSTALLATION/OPERATION MANUAL
5IM-OB-COM0-00
Mar/11
10
8.0 BLOCKED VENT SWITCH
Oil-fired appliances installed in Canada require a blocked vent shut-off system when installed
on a chimney. A safety switch is included with the furnace to perform this function. It is the
installer’s responsibility to install the switch in accordance with the instructions provided. Not
applicable for Direct Vent or Power Vent systems.
Field Controls Model: WMO-1 (Manual Reset)
Switch Operation
Blocked vent switches are flue gas safety devices for detecting spillage of flue gases due to a blocked
flue or inadequate draft. After detecting a problem, the switch de-energizes the system’s burner
control.
NEVER reset the switch unless the cause of the blockage has been corrected.
Installation
1) Pierce a 5/8” hole in to the flue vent pipe near the appliance breech connection.
2) This hole must be at least 10” before the draft regulator, vertically or horizontally.
3) Remove one of the securing nuts from the threaded tube of the safety switch.
4) Tighten the other securing nut onto the pipe as far as possible.
5) Insert the threaded tube end into the pierced hole of the flue vent pipe.
6) Install the securing nut on the safety switch tube, which protrudes into the flue vent pipe.
Tighten the nut securely.
Wiring Instructions
Caution:
Disconnect the electrical power when wiring the unit.
Wire the Blocked Vent Switch in accordance with The National Electrical Code and applicable local
codes. Wire the safety switch in series with the burner limit control or aquastat. Route the wiring with
an accepted wiring enclosure in accordance with the National Electrical code and applicable local
codes. Refer to wiring decal or Figure - 3.
System Test Procedure
1) With the power re-established, block the chimney or vent pipe downstream of the switch.
2) Adjust the thermostat to call for heat.
3) Once the heating system has started the blocked vent switch should shut down the
burner within 10 minutes or sooner.
4) Once the system has cooled, the blocked vent switch can manually be reset.
5) This procedure should be tested a second time.
6) After testing the blocked vent switch the chimney should be cleared of obstruction and the
heating system tested on a long run cycle.
If the block vent switch shuts down the system, check to ensure there is enough draft in the
chimney and venting pipes.
