Control Application Notes

"G" Heat exchanger Module

The GRE "G" Modules have a Multifunctional Gas Control Valve upon which options of control can be fitted.

Basic On/Off Control

High/low/Off control- two stage gas control & off

Pulse Combustion Control- with loose control unit & PT100 sensor

Mod 1 or 2 0-10V controller suitable for use with Building Management Systems

The unit's terminal strip has connections for incoming mains with a further pair for external safety controls such as air flow switches, external high limits etc. Further to these safety device facilities are the control circuit terminals which must be used for the temperature control circuit. These terminals correctly switch the Pactrol Gas Control Box.

On/Off & High Low Control

It is important when controlling any gas fired appliance that the control signal is positive and no hunting around the setpoint occurs, particularly which results in switchings within the Gas Flame proving and post extinguishing period of 1 minute. Gas control systems like stability and this should be considered when selecting the temperature controls Deadband or differential. With high/low control one should aim to switch to low flame with plenty of time for the systems thermal inertia to slow down to enable the low flame to effectively reduce the heat input with preferable switching back to high flame rather than off! A delay "on" timer relay is incorporated and set at 2 minutes, to prevent the rapid switching of the Control box and nuisance Lock Outs occurring.

Mod 1, 2 & Pulse combustion control

When the application is for Full Fresh Air, such as tempered make up air systems then serious consideration should be made for the-Pulse Combustion method of control, as described in our Pluse Combustion Control page.  This method of control is suitable for GTE, GRE & GTFE Modules only.

With a recirculating air and a Building Management control system 0-10V control is the usual method of heat to air control, the Mod 1 control method is described on our Mod 1 Combustion Control page.

The Lock Out system on the Modules is a function of the ionisation flame monitoring; the pilot when lit is constantly monitored by the flame rectification of the Pactrol Gas Control Box. If Lock Outs occur the unit has an integral illuminated-reset button, with the facility for running a pair of wires with Neutral to the remote control panel for remote Lock out reset, We strongly recommend the remote facility is wired in so that lock outs can be reset conveniently. Should Lock Outs become frequent then further investigations should be carried out. Lock Outs should not be ignored and all aspects of gas, power and control inputs should be checked. Very often lock outs occur due to external influences; the control box probe circuit is very reliable when properly commissioned.

High temperature protection is included on the unit with two thermostats one of which is self resetting for occasional occurrences. With the second for manual resetting set at a higher temperature the Air Handling Unit MUST include integral air flow detection to prevent constant overheating of the heat exchanger and a fan run on timer to enable the heat exchanger to cool down at the end of the day.

With the correct choice of burner and proper consideration of the external control system the Gas Burner control will give good reliable service. We would be happy to advise further, please do not hesitate to ask.


  1. Explanation of Heat Exchanger Modules
  2. Control Application Notes
  3. Flue Application Notes
  4. Pulse Combustion Control
  5. Mod 1 Combustion Control

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