A.O. Smith FMD 40 Manuale Utente

17

A sediment trap shall be installed as close to the inlet of the water 
heater as practical at the time of water heater installation. The 
sediment trap shall be either a tee fi tting with a capped nipple in the 
bottom outlet or other device recognized as an effective sediment 
trap. If a tee fi tting  is used, it shall be installed in conformance with 
one of the methods of installation shown in Figures 27, 28 and 29. 

                

       

           

Contaminants in the gas lines may cause improper operation of 
the gas control valve/thermostat that may result in fi re or explosion.  
Before attaching the gas line be sure that all gas pipe is clean on 
the inside.  To trap any dirt or foreign material in the gas supply line, 
a drip leg (sometimes called a sediment trap) must be incorporated 
in the piping.  The drip leg must be readily accessible.  Install in 

accordance with the “Gas Piping” section. Refer to the current 
edition of the Natural Gas and Propane Installation Code (CAN/CSA 
B149.1-current edition). 

This water heater has been factory equipped to operate with the 
type gas indicated in the “EQUIPPED FOR” area of the model rating 
plate located near the gas control valve/thermostat. The indicated 
gas may be either Natural or Propane (L.P.). By following the 
conversion instructions in this manual or the instructions near the 
gas control valve/thermostat, the water heater must be converted if 
it is to be used with the opposite gas. DO NOT USE THIS WATER 
HEATER WITH ANY GAS OTHER THAN THE ONE LISTED ON 
THE MODEL RATING PLATE. Failure to use the correct gas can 
cause problems which can result in DEATH, SERIOUS BODILY 
INJURY, OR PROPERTY DAMAGE. If you have any questions or 
doubts consult your gas supplier or gas company. 

Read and follow detailed conversion instructions located on the 
water heater and also in the instruction manual in their entirety before 
starting the conversion.

Conversion kit with necessary parts are in a bag attached to the 
drain valve.

Orifi ce size: #40 for Natural / #52 for Propane (L.P.), 
if converted - Propane Rate: 30,000 BTU.

Orifi ce size: #38 for Natural / #51 for Propane (L.P.), 
if converted - Propane Rate: 32,000 BTU.

Orifi ce size: #35 for Natural / #51 for Propane (L.P.), 
if converted - Propane Rate: 38,000 BTU.

Step 1.  Turn gas control knob “A” to “PILOT”. Depress and turn 

“OFF”, see Figure 30 page 19.

Step 2.  Remove outer and inner access doors from water 

heater.

Step 3.  Remove burner assembly from water heater control 

by fi rst removing 6 screws holding inner door to heater, 
then loosening 3/4” nut “H” holding burner assembly to 
control, see fi gures 31 and 32. Loosen pilot tube nut “J” 
and thermocouple nut “K” at control. Disconnect wire to 
Piezo Igniter.

Step 4.  Remove screws “D” disengaging manifold from burner, 

see Figure 33 page 19.

Step 5.  Remove orifi ce “E”, see Figure 34 page 19 using 3/8” 

wrench. Install orifi ce marked “L.P.” found in the bag into 
manifold. Tighten securely. Secure burner to manifold with 
screws “D”.

Step 6.  Loosen pilot tube nut “F”, see Figure 34 page 19. Remove 

orifi ce “G” and replace with red colored orifi ce found in bag. 
Reinstall nut “F” and tighten securely.

Step 7.  Make  sure  all connections are tightened securely, and 

reinstall burner assembly into water heater. Position end 
of manifold inside bracket as shown in Figure 33 page 
19. Reinstall manifold into control and tighten 3/4” nut 
(“H”) securely. Recheck to see that end of manifold is still 
inside bracket as shown in Figure 33 page 19. Reinstall 
pilot tubing and thermocouple into control, see Figure 31 
page 19. Connect wire to Piezo Igniter. Reinstall inner door 
using the 6 screws removed in Step 3.