Heat-Timer® Corporation


Condensing and Non-Condensing Outdoor Reset Modulating Boiler Control


The Mini-MOD-CNC is an outdoor reset multiple boiler heating control.  It operates two different groups of boilers, condensing and non-condensing.  It operates both modulating and multi-stage boilers. It changes the lead boiler group to condensing when the system target temperature is below a specified switching set point.  However, when the system target temperature rises above the switching set point, the Mini-MOD-CNC will switch the lead boiler group to the non-condensing.  This design evolved from heating applications need to increase their operating efficiencies while reducing their equipment initial investment.

System Target Temperature Switching of Lead Group: The Mini-MOD-CNC uses a target switching set point with an adjustable switching delay. If  the target temperature was below the switching set point, the Mini-MOD-CNC will use the condensing boiler group as the lead boiler group. If the target temperature rises above the switching set point for a specified delay period, the Mini-MOD-CNC will switch the lead boiler group from the condensing to the non-condensing lead boiler group.

Parallel or Normal Modulation: For the modulating group of boilers (condensing or non-condensing), an advanced PID logic has been used to provide an efficient, smooth, and adjustable modulation that can fit most applications whether the boilers are to sequence normally, one after the other, or in parallel. With numerous configurable parameters like Ignition %, Modulation Start %, Gain, Lag Delay, Soft-Off , and Last Stage Hold, the PID logic can be adjusted to meet any building specific heating application.

Domestic Hot Water Control with Optional Priority  It can be configured with Domestic Hot Water call option. It will increase system water temperature when Domestic Hot Water is needed. In addition, it allows for optional priority of the domestic hot water over heating.

  • Hybrid Operation, operates a condensing group and a non-condensing group
  • Each of the two groups of boilers can be either modulating or staging
  • Built-in outdoor reset
  • Add up stages using up to two Mini-Extension Panels (each can control up to 6 stages) up to 16 total stages
  • Built-In Day/Night Schedule for with an adjustable setback
  • Domestic Hot Water capability with optional priority
  • Multiple lead rotation options including an automatic lead rotation of up to 999 hours
  • Remote enable/disable capability
  • Now with setback and boost functionality for better comfort and energy saving
  • Mini-MOD-CNC is UL listed
  • Mini-MOD-CNC is NYC DEP Approved (DEE #2-03)
  • Locking NEMA-1 compliant enclosure
  • Comes complete with Outdoor Sensor and System Sensor

The Mini-MOD-CNC comes complete with both the System and the Outdoor sensors.

Mini-MOD-CNC 926743-00
Mini-Extension (adds 6 stages) 926712-00
4-20mA EMS Interface (adds remote 4-20mA set point) 926741-00

Connected the control to power correctly but no display or LED is on.
Most controls are equipped with a fuse on the back of the main board to help protect the control against power surges. Check the fuse on the back of the control using a continuity meter. If continuity does not exist, replace the fuse with the same fuse size and rating.

My hot water outdoor reset control is giving me too much heat. What should I do?
Check if the control has any of the following: •Reset Ratio and Offset – If excessive heat occurs only in certain weather conditions, adjust the Reset Ratio and Offset. If excessive heat occurs year round, reduce the Offset. •Boiler Mode Settings – The control will only operate boilers their mode is set to Auto or Standby. Check to if any boiler stage is set to Manual or On. •Multi-Stage Control Settings – The Last-Stage-Hold will allow only the Lead boiler to stay on for an additional number of degrees. If the setting is too high, and only the Lead boiler is on, the system can over heat. Reduce the Last-Stage-Hold setting. •Domestic Hot Water Call – On a DHW call, the System Set Point will rise to the DHW Set Point or 200°F. If the increase in temperature is during DHW call, see about using any of the DHW Priority options available on the control.

Why is my control not turning the boiler on even when there is a call for heat?
First, check the display for any messages as many of the heating controls have several external inputs that can be used to shutdown the boiler. If the message relates to the PROVE input, it may not be shorted or the Prove terminal Jumper is not installed. In this case, the control will not start the boiler. If the message relates to the Shutdown input, the Shutdown maybe shorted remotely. If the message relates to the T-stat input, the T-Stat input maybe opened remotely.

My outdoor sensor reading does not match the actual temperature.
The outdoor sensor measurement may vary based on its location and its sun exposure. In most cases it will never match a weather station that is located several miles away. most current Heat-Timer controls have a Trim feature which allows the sensor reading to be slightly modified just a few degrees to satisfy similar circumstances. If the difference was large, then check the sensor by disconnecting one of its wires from the control. The control should read OPEN. If not, contact technical support.

Why is my temperature sensor reading Open on the control display?
Remove the sensor wires from the control and check for continuity across the wires with and meter. If no continuity existed, check or replace the wires. if continuity did exist, then contact technical support.

Why is my temperature sensor reading Short on the control display?
Remove one of the sensor wires from the control. The control display should change and display OPEN. Then check the sensor wiring specifically around spliced areas. If wiring was good, then disconnect the sensor wires from the control and check the sensor wires with an Ohm meter. The readings should match the sensor temperature chart on the control manual. It not, then replace the sensor. If after removing one of the sensor wires the control read SHORT, then contact tech support.

Why does my Heat-Timer hot water reset control (HWR) flash OPN instead of the outdoor temperature?
Heat-Timer controls use the code OPN when they can not detect a sensor. For example, if someone were working in the building and cut the wires leading to the outdoor sensor, the HWR would begin to flash OPN to signal that the sensor was no longer attached. To find the source of the OPN reading, first make sure that the outdoor sensor wires are attached to the input terminals (the IT terminals in the case of an HWR). Then place a jumper wire across the input terminals (IT). The display should change to read SH-I (the code for a shorted sensor). If the display does change, the HWR is working properly. Check the wires to make sure they are not broken, and locate the sensor to see if it has been damaged.

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