Remington HH-70T-KFA Service Manual download pdf (Page 122)

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Gas Fired Heaters

Component Description and Operation

Thermocouple

The thermocouple is a safety feature that works with a thermoelectric gas valve to allow or

interrupt the flow of fuel. The thermocouple works on a principle of two dissimilar metals, that

generates D.C. electricity, when heated. Because of this technology, it is important that the

thermocouple’s sensing bulb is in the hottest portion of the flame pattern to work properly. The

D.C. electricity is rated in millivolts. The D.C. electricity passes down the thermocouple until it

reaches the power coil located inside of the thermoelectric gas valve. The thermocouple needs to

generate and send at least 17 millivolts of D.C. electricity to the thermoelectric gas valve to keep

the power coil compressed or energized, and let allows gas to pass through. A thermocouple

may also have an electrical interrupter connection. An electrical interrupter connection is an

electrical interrupter located between the tip of the thermocouple and the nut that threads into the gas valve. The purpose of this

interrupter is that it allows the manufacturer to install a safety feature on the thermocouple to break the D.C. circuit in case of a unit

malfunction. The most common use of the interrupter connection is to install a high limit switch. For example, if your heater has a

high limit switch attached to the interrupter, and the switch gets too hot, the limit switch will open up contacts and break the polarity

between the thermocouple and power coil, thereby shutting down the flow of fuel.

D.S.I. Control

Some people call this part the “brain box” of the heater. Actually, D.S.I. stands for Direct Spark

Igniter. However, this part controls a lot more than ignition. It controls the following circuits.

Ignition - The board produces the secondary voltage during the ignition process.

Flame sensing - The board monitors the flame through a spark plug, electrode, or flame rod.

Electronic delay timer (pre-ignition purge cycle).

Supplies the solenoid circuit with power.

The most common brand names for D.S.I. controls are:

Ram controls - Ram controls have come in three different colors, blue, white, or gray.

Gaslighter controls - Gaslighter boards have usually been black in color.

Fenwall controls - Fenwall controls are usually gray in color.

The last point to mention about D.S.I. controls is that if you have one in your heater, two things are true. 1) your heater can use a

thermostat, and 2) your heater will not have a thermocouple.

Gas Valves

Gas Valves are used for two main purposes. The first is to shut off the flow

of fuel in case of malfunction, the second is to determine manifold gas

pressure.

There are two different types of gas valves (thermoelectric & solenoid) used in

portable heaters.

Thermoelectric - Thermoelectric gas valves work on the principle of D.C. voltage being generated by a thermocouple. Thermoelectric

valves are sometimes known as the “push button” valves. The thermoelectric valve receives the D.C. voltage generated by the heated

thermocouple and then energizes (magnetizes) the power coil located inside of the valve body. The power coil

needs this voltage to stay compressed (magnetized) to allow gas to flow through to the burner. The minimum

voltage required to keep the power coil energized is 17 millivolts of D.C. electricity.

Solenoid valves - Solenoid valves require A.C. voltage (usually 120 volts) to electronically close, and to physically

open. When the solenoid valve closes, it is actually electronically closing (magnetizing) the coil to allow gas to flow

thru. Power to the solenoid valve never comes directly from the cord. It usually passes through a D.S.I. control first.

By passing through the D.S.I. first, it allows the D.S.I. to shut off the voltage to the solenoid if it senses a problem

such as an open electrical circuit, lack of flame sensing, or lack of fuel to name a few.

Thermocouple with

Interrupter

Thermoelectric Valve with Power Coil

Solenoid Valve

Gas Heater Service Info.

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Remington HH-70T-KFA Service Manual Page 122

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