Servicing a Conversion Gas Burner
Always be sure that the manual gas valve and burner switch are turned off before attempting to service a gas burner. Never attempt to remove any parts for service before taking this precaution.
In direct spark ignition burners, the nozzle and electrode assembly can usually be removed as a unit. For example, the nozzle-and- electrode assembly of the Economite Model DS20A conversion gas burner can be completely removed in the following manner:
1. Remove the burner backplate.
2. Disconnect the pipe union.
3. Remove the curved orifice pipe.
4. Withdraw the nozzle assembly.
5. Disconnect the electrode leads.
6. Remove the unit.
The nozzle-and-electrode assembly can be reinstalled by revers- ing steps 1 through 6. When reassembling, make certain the orifice pipe enters the nozzle casting.
With the nozzle-and-electrode assembly completely removed, you are now in a position to inspect and clean it. Check the electrode for insulator cracks and evidence of serious burning.
Removal of the burner backplate also provides access to the motor and blower, motor relay, low-voltage transformer, and terminal board. These can be removed as a unit for servicing, but you will have to disconnect the terminal board and unplug the electrical pass-through fitting to do this. The following service may be required for this unit:
1. Cleaning of the blower wheel.
2. Cleaning the motor air vents.
Does the motor run without further burner sequencing taking place? This may indicate trouble in the centrifugal interlock switch. Some burners are provided with removable motor end caps to provide ready access to the centrifugal switch. If this should be the case, remove the cap and clean the contacts by burnishing. The contacts must be open when the motor is not operating. If necessary, the burner motor can be removed and replaced as follows:
1. Remove the blower wheel.
2. Remove the retainer clips at the motor grommets.
3. Pull the motor out of the brackets.
4. Repair or substitute a new motor.
5. Place motor in brackets.
6. Make certain grommets fit well in the bracket and replace retainer clips.
7. Replace blower wheel.
The sealed motor relay and low-voltage transformer normally do not require servicing. They should be replaced when defective.
Check gas lines and valves for leaks with the soapsuds test. Never use a flame to locate a gas leak. If the leakage occurs around the valve, the valve seat may need cleaning. Disassemble the valve, clean the seat, and reassemble it. If the valve malfunction is due to causes other than the seat, replace the entire valve.
Replace the gas pressure regulator if it fails to maintain a constant pressure. On the conversion gas burner illustrated in Figure 16-14, the regulator is part of a combination valve (in this case, a Robertshaw 24-volt combination gas valve), but it is designed so that it can be replaced without replacing the entire assembly.
Pressure adjustment required for setting intermediate capacities can be accomplished as follows:
1. Remove the adjustment screw cap.
2. Take a screwdriver and turn the adjustment screw counter- clockwise to reduce pressure.
3. Measure the pressure through the manometer connection adjacent to the outlet tapping.
Conversion gas burners equipped with a pilot light require inspection and servicing of the following:
1. The pilot orifice size will depend upon the type of gas used.
For the conversion gas burner illustrated in Figure 16-13, the pilot orifice will have a diameter of 0.018 in for natural gas and 0.012 in for propane.
2. Set the end of the burner nozzle at least 1 inch short of the inside of the combustion chamber (see Figures 16-15 through 16-18). It must not be set flush with the chamber or be allowed to extend into the chamber (the pilot is often snuffed out in such cases by recirculated flue products).
3. Check for a high or low gas pressure. If over 7 inches W.C., reset the pilot adjustment (see Figure 16-13) to reduce the size of the pilot flame and to increase the heat on the thermo- couple.
The thermocouple and pilot-safety section of the main valve should be tested to determine whether they are operating efficiently. The testing procedure is as follows:
1. Turn the burner switch to OFF.
2. Allow the combustion chamber to cool and the pilot light to operate for at least 5 minutes.
3. Turn off the pilot and listen for a “click” from the main valve.
4. If the “click” of the main valve is heard more than 30 seconds after you have shut off the pilot, then both the thermocouple and the pilot-safety section of the main valve are operating efficiently.
5. If the “click” occurs less than 30 seconds after you have shut off the pilot, then either the thermocouple or pilot-safety section of the main valve is faulty.
6. Test the thermocouple by disconnecting it from the main valve and checking it with a millivoltmeter. Under normal conditions (i.e., when heated by a standby pilot), it should develop at least 15 millivolts.
7. If the thermocouple develops at least 15 millivolts but the main valve “click” still occurs less than 30 seconds after you have shut off the pilot, the pilot-safety section is probably malfunctioning.
8. The thermocouple may also be tested while still connected to the valve (a closed-circuit connection) by using an adapter to connect the millivoltmeter. Under normal operating condi- tions, the thermocouple should develop at least 7 millivolts and the valve 4 millivolts.
The wiring diagram for a conversion gas burner equipped with a pilot light is shown in Figure 16-19. The installation and service instructions from most manufacturers will include a wiring diagram for the burner. Study it carefully before servicing or making repairs.