Gas Heat System Theory of Operation

Purpose

The F5 gas heat system uses an induced draft burner to heat cooking oil in each vat. It pulls hot combustion gases through vat heat exchanger tubes and out the exhaust flue, ensuring safe and efficient heat transfer. This airflow is essential to keep flames inside the heat exchanger tubes and prevent misdirected combustion.

System Overview

What It does

• Heats cooking oil using combustible gas.

• Controls ignition and flame safety through sensors and modules.

• Uses induced airflow to guide combustion gases through the heat exchanger.

Subsystems Breakdown

Inputs

These are the signals and supplies that allow the system to operate:

• Combustible Gas Supply

  • Source of fuel for the burner.

• GMU Safety Circuits

  • Ensure safe operation before allowing ignition.

• Oil Temperature RTD Probe (per GMU)

  • Measures oil temperature to determine heating needs.

• Ignition Module Signals

  • PV (Pilot Valve): 24V signal to open pilot valve.

  • MV (Main Valve): 24V signal to open main burner valve.

• Flame Rollout Sensor (per GMU)

  • Detects if flame escapes the burner area (safety check).

Outputs

These are the actions the system takes based on inputs:

• 24V DC to BCB (Blower Control Board)

  • Powers the combustion fan to create airflow.

• 24V AC to Ignition Module TH (Thermostat)

  • Activates ignition sequence.

• 24V AC to Safety Shutoff Valve (CE only)

  • Cuts gas flow in unsafe conditions.

• 24V AC to Pilot Valve

  • Opens to allow pilot flame ignition.

• Pilot Flame Ignition

  • Small flame that lights the main burner.

• 24V AC to Main Valve

  • Opens to allow full burner ignition.

• Gas Burner Ignition

  • Main flame heats the vat.

• Heating of Cooking Oil

  • Final result: oil reaches target temperature.

How it all Work Together

1. Start-up Sequence:

• Control system checks safety circuits.

• Combustion fan starts (via BCB).

• Pilot valve opens → pilot flame ignites.

• Flame rollout sensor confirms safe flame location.

• Main valve opens → burner ignites.

• Heat exchanger warms oil.

2. Temperature Regulation:

• RTD probe monitors oil temp.

• If oil is below set-point, burner re-ignites.

• If oil is at set-point, burner shuts off.

3. Safety Monitoring:

• Flame roll-out sensor detects unsafe flame behavior.

• Safety shutoff valve closes if needed.

• GMU safety circuits prevent ignition if faults are present.

Technician Tips – “Think Like the Equipment”

No Heat?

• Check for 24V signals to ignition module and valves.

• Confirm combustion fan is running—no airflow means no ignition.

Pilot Won’t Light?

• Verify pilot valve is receiving 24V AC.

• Check flame rollout sensor for faults.

Burner Ignites but Oil Doesn’t Heat?

• Confirm RTD probe is reading correctly.

• Check for proper flame inside heat exchanger tubes.

Flame Rollout Trips?

• Inspect for blocked airflow or damaged burner components.

Intermittent Heating?

• Look for loose connections at ignition module or RTD probe.