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Propane Service Opportunities

This Chapter contains information on:

• Propane Burners and Air Circulating Service Problems
• Testing Thermocouple under Operating Conditions

Propane Burners and Air Circulating Service Problems

The following service problems and possible corrections have been listed to assist member cooperative personnel in handling service corrections on space and central heating systems. (Causes may not be listed in order of importance.)

1. Ignition at burner orifice, in Ventura, or noise on ignition.

1. Improper fuel-air adjustment.
2. Orifice not centered in Ventura opening.
3. Orifice drilled off-center.
4. Too-high gas pressure.
5. Too-low gas pressure.
6. Sluggish automatic gas valve.
7. Drill burr in orifice.
8. Dirt in orifice.

2. Pilot outage

A thermocouple failure or loss of differential temperature usually causes this symptom. A short explanation of how a thermocouple is manufactured or operates, for those of you who may not know, follows…..

A thermocouple is manufactured by welding at one end two dissimilar metals, which will be known as the hot junction. The other ends will be known as the cold junction., In most all thermocouples, the distance from the hot to the cold junction will be ¾" to 3 inch. However, the connecting leads from the thermocouple to the control valve can vary from a few inches to feet. When a pilot flame is applied to the top 3/8" of the hot junction, a voltage in milli-volts is produced and can be measured across the cold junction using a Mil-Volt meter where the thermocouple leads connect with the 100% valve. The amount of voltage depends on the following…..

1. Differential temperature between the hot and cold junction. The greater the differential, the higher the voltage will be.
2. Types of dissimilar metals used in manufacture.
3. Length of thermocouple, hot to cold junction.

All heating equipment is designed with 100 % safety valves that operate with normal voltages that can be produced with a normal pilot flame when the specification thermocouple is used.

To test a thermocouple under operating conditions, use the following procedure….

1. Disconnect thermocouple connection at 100% Safety Valve.
2. Using Baso Model 120 Meter, or similar meter, connect proper test lead to thermocouple connection in 100% Safety Valve.
3. Plug test lead into mil-amp jack on meter.
4. Set meter control knob on 30MV scale.
5. Depress or turn 100% safety valve button and light pilot burner. Batteries in meter will hold 100% Safety Valve open and allow pilot to burn. Plug test lead with two alligator clips into mil-volt jack on meter.
6. Attach red clip to outside of the thermocouple lead and the black clip to the tip end of the thermocouple lead below the insulated washer.
7. Attach red clip to outside of the thermocouple lead and the black clip to the tip end of the thermocouple lead below the insulated washer.
8. Check manual for correct reading. If normal, thermocouple is o.k.; If reading is near or below minimum, check pilot flame on thermocouple. Flame should impinge on thermocouple in the top ¼" to 3/8". If not adjust and recheck meter reading. If reading is still at or below minimum replace thermocouple and recheck with meter.
9. When thermocouple has checked o.k., turn on main burner. Watch meter as main burner operates. Meter should drop a few points and hold. As meter begins to fall - check combustion chamber for heat being reflected or conducted into the thermocouple, causing a loss in differential temperature and a lower voltage being developed in thermocouple.
10. Reflected heat can be corrected by installing a shield around the thermocouple.
11. Conducted heat can be corrected by installing a piece of insulation between the pilot thermocouple bracket and the burner.
12. Recheck with meter.  Step #9 should be o.k.

3. Noise on shut-down of burner

1. To high pressure
2. Sluggish automatic gas valve
3. Improper air-fuel adjustment

4. Furnace will not fire-pilot burning

1. Fuse blown or loose.
2. Furnace switch in off position.
3. Thermostat inoperative – contact burned or dirty.
4. Loose connection or broken wire between thermostat, solenoid, high limit switch or transformer.
5. Transformer burned out.
6. Solenoid valve inoperative.
7. Defective high limit switch.

5. Furnace will not fire – pilot out

1. Supply tank empty.
2. Regulators inoperative.
3. Thermocouple failed.
4. Pilot dirty.
5. Pilot improperly adjusted to thermocouple.

6. Furnace fan runs most of the time but home is cold

1. Air filter plugged.
2. Fan switch improperly adjusted.
3. Improper gas pressure.
4. Improper fuel air adjustment.
5. Heat exchanger partly blocked.

7. Home cold –burner cycles on and off

1. Fan switch inoperative.
2. Fan belt broken off or too loose.
3. Fan motor burned out.
4. Fan pulley loose on shaft.
5. Motor pulley loose on shaft.
6. Blower pulley loose on shaft.
7. Blower shaft bearing frozen.
8. Weak high limit switch.

We have tried to cover most of the common causes of heating problems. We know you could encounter others; however, in checking the above conditions, you will most likely find the problem and correction.

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