Revised Wiring Diagrams for Single and Multi-Zone Switching Relays
Clarification of Potential Safety Hazard
A possible safety hazard exists for technicians and other
installers when using switching relay controls with an oil-fired boiler
with tankless coil. This potential hazard exists when using switching relay controls from any manufacturer, including those made by Taco.
The hazard exists if two separate sources of power are connected to an
oil burner's aquastat control. When servicing the boiler, a technician
may think that he has shut off all power to the boiler at the service
switch, when in fact a secondary source of power may be wired directly
to the aquastat through the switching relay. In
these circumstances, if a zone calls for heat, sending power form the
switching relay directly to the boiler, the technician could be injured.
Please note: This potential hazard exists only on oil-fired boilers with a tankless coil because they require a line voltage demand signal to be turned on.
Whenever servicing an oil burner, technicians should always check for two power sources by determining:
1. Is power from the circuit breaker wired directly to the switching relay?
2. Is line voltage supplied by the switching relay wired directly to the boiler aquastat?
Taco has changed its wiring diagrams and added warnings on
its instruction sheets to alert technicians of this potential hazard.
However, please keep in mind that this potential safety hazard exists
with single and multi-zone switching relays produced by any
To download the revised Zone Control Wiring Guide in PDF format, please click here.
To have a free printed copy of the Zone Control Wiring Guide mailed to you, please click here.
To download the safety notice (including additional wiring diagrams) in PDF format, please click here.
To have a free printed copy of the safety notice mailed to you, please click here.