Intermittent Ignition Oil Primary: A Basic Guide

An intermittent ignition oil primary (IOP) is a device that controls the operation of an oil-fired burner in response to a call for heat. It also monitors the flame and shuts off the system in case of flame failure or loss. An IOP is typically used in residential oil-fired boilers, furnaces, water heaters, and other appliances where pre/post-purge is not required for safety.

How does an IOP work?

An IOP consists of three main components: a control board, a flame detector, and a safety switch. The control board receives input signals from a thermostat and a cadmium sulfide (cad cell) flame detector, and sends output signals to the oil valve and the ignition transformer. The flame detector senses the presence or absence of flame using a photoresistive cell that changes its resistance depending on the light intensity. The safety switch is a manual reset button that interrupts the power supply to the control board in case of a lockout condition.

The operation of an IOP can be summarized as follows:

  • When there is a call for heat, the control board energizes the oil valve and the ignition transformer, and starts a safety timing period (usually 30 or 45 seconds).
  • The oil valve opens and allows oil to flow to the burner nozzle, where it is atomized and mixed with air. The ignition transformer generates a high-voltage spark that ignites the oil-air mixture and creates a flame.
  • The flame detector senses the flame and sends a signal to the control board, which de-energizes the ignition transformer and keeps the oil valve open. The burner continues to operate until the call for heat is satisfied.
  • If the flame detector does not sense a flame within the safety timing period, the control board de-energizes the oil valve and the ignition transformer, and enters a lockout mode. The safety switch opens and cuts off the power to the control board. A status indicator LED on the control board flashes to indicate a lockout condition.
  • To reset the system, the user has to press and hold the safety switch for three seconds, and then release it. The control board will resume normal operation and attempt to restart the burner.

What are the advantages of an IOP?

An IOP offers several benefits over a continuous ignition oil primary (COP), which keeps the ignition transformer energized throughout the burner cycle. Some of the advantages are:

  • Reduced energy consumption and cost: An IOP only uses the ignition transformer for a short period of time, which reduces the electrical load and the power bill.
  • Increased safety and reliability: An IOP prevents the ignition transformer from overheating and wearing out, which reduces the risk of fire and malfunction.
  • Improved performance and efficiency: An IOP ensures a stable and consistent flame, which improves the combustion quality and the heat output.

What are some examples of IOP models?

There are many IOP models available in the market, each with different features and specifications. Some of the popular ones are:

  • ICM1503: This is an IOP model from ICM Controls that has a safety timing of 45 seconds. It features a solid state flame sensing circuit, an LED to indicate system lockout, an enclosed safety switch with external reset button, and a standard 4×4 junction box mounting. It is a direct replacement for Honeywell R8184G series, Carlin 48245, Tempstar/Heil 1147017, and White Rodgers 668-401.
  • ICM1502: This is another IOP model from ICM Controls that has a safety timing of 30 seconds. It has the same features as the ICM1503, except for the safety timing. It is also a direct replacement for the same models as the ICM1503.
  • R7284U: This is an IOP model from Honeywell that has a universal safety timing of 15 or 30 seconds, selectable by the user. It features a digital display that shows the status and fault codes, a data port that allows communication with a diagnostic tool, an adjustable valve-on and motor-off delays, and a universal mounting bracket. It is a direct replacement for Honeywell R7184A, B, P, U, and R7284B, P, U.

How to compare different IOP models?

To compare different IOP models, one can use a table that shows the main characteristics and specifications of each model. For example, the table below compares the three IOP models mentioned above.

Model Safety Timing Flame Sensing Status Indicator Reset Button Mounting Replaces
ICM1503 45 seconds Solid state LED External 4×4 J-Box or direct Honeywell R8184G series, Carlin 48245, Tempstar/Heil 1147017, White Rodgers 668-401
ICM1502 30 seconds Solid state LED External 4×4 J-Box or direct Honeywell R8184G series, Carlin 48245, Tempstar/Heil 1147017, White Rodgers 668-401
R7284U 15 or 30 seconds (selectable) Solid state Digital display Internal Universal bracket Honeywell R7184A, B, P, U, and R7284B, P, U

The table can help the user to choose the best IOP model for their needs, based on the safety timing, the flame sensing method, the status indicator type, the reset button location, the mounting option, and the compatibility with other models.

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