Heat-Timer® Corporation


Outdoor Reset Modulating Boiler Controls for Hydronic Heating Systems


Outdoor Reset Modulating Boiler Control.

The Mini-Mod is an outdoor reset modulating boiler control. It is the perfect control whenever multiple fully modulating hot water boilers are used in building heating applications. The Mini-Mod controls the on/off and the modulation of each stage to maintain precise set point control using PID type control logic.

Controls 0-5 V, 0-10 V, 1-5 V, 2-10 V, or 4-20 mA modulating motors.

The Mini-Mod is the perfect modulating boiler control as it is designed to accurately modulate the output from 0 to 100% of modulation for each of these different types of boilers / motors. One Mini-Mod can even control any combination of the above types of motors.

Digital Display of all System Settings.

The Mini-Mod’s graphical display names each system parameter in plain English and shows its precise value. The easy to follow menu system allows user to quickly make changes to any system setting without having to learn any specialized codes or keyboard commands. Protection is available to prevent unauthorized users from making adjustments to control settings using an enclosed switch that can be locked.

Automatic Rotation among States.

The Mini-MOD has a variety of boiler Rotation options. Thus, offer muliple way to rotate the boilers to promote even wear on each boiler. The Mini-Mod has three modes of rotation : Manual, Last-On, or automatically every selected time period from every hour to every 60 days in one hour increments.

Outdoor Reset Capability.

The Mini-Mod can be connected to existing or new Heat-Timer outdoor reset controls (HWR Platinum for hot water heat). The Mini-Mod also has built in hot water reset with adjustable reset ratios, offset, outdoor cutoff, minimum and maximum water temperature.

Temperature Set Point or EMS Option.

The Mini-MOD canbe set to modulate boilers to achieve a fixed set point. Moreover, using the 4-20mA EMS Interface, it can accept a set point from an EMS system.

Parallel or Normal Modulation.

An advanced PID logic has been developed 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; Last Stage Hold and Soft-Off to eliminate the lead boiler short cycling; Lag Delay to eliminate lag boilers short cycling. The PID logic can be adjusted to meet your specific heating application.

Connects to Energy Management Systems.

All Mini-Mods can be disabled by an Energy Management System(EMS) or other controller when there is no output requirement. Moreover, using the 4-20mA EMS Interface, the Mini-MOD can accept a set point from an EMS system.

Day and Night Schedule or Setback.

The control has an adjustable Night Setback setting to help reduce fuel consumption. The built-in schedule can be used to customize the operation for even further temperature control and fuel savings. Furthermore, the Mini-Mod provides an alternative Setback option for applications that rely on other equipment and controls.

System Output is Active with Stages with an Adjustable Delay.
This output can be used to activate a system pump, combustion air damper, or perform any other function that is required when any stage is active. A System Prove input checks the status of components activated by the System output before stages can be activated. An adjustable delay is available to disburse additional heat in boilers.

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.
Optional, Digital Boiler Signal Converter to 0-10V.
The 0-10V Converter allows modulating boilers with a digital signal to be controlled by the Mini-MOD. It can be purchased separately.

Additional features include:

A purge timer, a low fire adjustment (Ignition %), a firing point setting (Modulation Start %) for the next stage based on the firing rate of the current stage, a lag stage timer, a last stage hold adjustment, a Soft-Off that holds a stage for a period of time before turning off, and many others.

  • Built-in outdoor reset
  • Digital display of: System temperature, system set point, and control parameters
  • The option of using outdoor reset, set point, or receive an external set point from an EMS/BMS system as 4-20mA (requires the use of 4-20mA EMS Interface)
  • Display of percent modulation of each stage
  • Manual overrides for each stage
  • Automatic or manual lead stage rotation
  • Can be cascaded to provide as many stages as needed using up to two Mini-Extension Panels (each can control up to 6 boilers) up to a total of 16 boilers
  • RWB mod motor output (0-5 V, 0-10 V, 1-5 V, 2-10 V, and 4-20 mA) and N.O. contacts for each stage
  • Can be field configured for remote setback or based on the control’s Day/night Schedule
  • Domestic Hot Water capability with optional priority
  • Solid state sensors can be extended up to 500′ from the control
  • Locking NEMA-1 compliant enclosure
  • Mini-MOD-CNC is UL listed
  • Mini-MOD-CNC is NYC DEP Approved (DEE #2-03)

ModelsThe Mini-MOD comes complete with outdoor and system sensors.

Mini-MOD 926710-00
Mini-Extension 926712-00
4-20mA EMS Interface 926741-00
0-10V Converter Module 926740-00

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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