30
2. Shut off gas upstream of heater.
3. Remove front door.
4. Disconnect gas line from gas valve.
5. Remove (2) screws that mount burner tray to unit,
and (2) screws that secure gas valve to jacket.
6. Disconnect wires that terminate at gas valve.
7. Disconnect hi-tension wire from PC board.
8. Slide out burner tray.
9. Reverse above procedure to reinstall.
8.5.9. Gas Valve Removal
1. Shut off gas supply to the heater. Remove gas piping
to gas valve inlet.
2. Disconnect wires, pilot tubing and bleed line, if
required.
3. Remove burner tray from heater.
4. Turn vertical gas pipe from manifold slightly and
unscrew gas valve.
5. Reverse above procedure to reinstall.
8.5.10. Main Burner And Orifice Removal
1. Remove burner tray.
2. Remove screws and burner hold-down bracket.
NOTE:
If the heat exchanger is sooted badly, the burner
hold-down bracket and spacer can become distorted from
direct-flame impingement and this usually necessitates
replacement of these parts.
3. Lift burners from slotted spacers and slide from
orifices. Clean with a wire brush.
4. Orifices usually do not need to be replaced. To clean,
run either copper wire or wood toothpick through
orifice. Do not enlarge hole. To remove orifice, use a
socket wrench and remove from manifold. DO NOT
overtighten when reinstalling.
GAS
ORIFICE
GAS VALVE
PILOT
BURNER
BURNER
HOLD-DOWN
BRACKET
Figure 49. Burner Tray Assembly
8.5.5. Flame Roll-Out Safety Switch
The heater is equipped with a thermal cutoff device to
prevent flame roll-out in the event the heat exchanger
becomes blocked. This is a “single-use” type fusible link
or thermal fuse, that must be replaced when disabled
by an over-temperature condition, caused by excessive
restriction in the heat exchanger flue passage.
Figure 47. Flame Roll-Out Safety Switch
8.5.6. High Limits
The heater is equipped with two automatic high limits.
One is located in the inlet/outlet header, and the other is
located in the return header. Both are set to open at 135°F
(57°C).
NOTE:
An erratic high limit is often characteristic of an
internal heat exchanger problem, e.g. scale build-up,
defective bypass. Refer to Troubleshooting section.
Figure 48. High Limit Switch
High Limit Removal
1. Shut off main electrical power switch to heater.
2. Remove inlet/outlet and/or return inspection panel.
3. Remove defective high limit and replace with a new
high limit.
4. Replace inspection panel.
8.5.7. Pilot Safety
The heater employs a pilot safety which closes the main
gas valve within 8/10ths of a second whenever the pilot
flame is interrupted. The pilot flame is automatically lit
when the device is powered. The heater performs its own
safety check and opens the main valve only after the pilot
is proven to be lit.
8.5.8. Burner Tray Removal
1. Shut off main electrical power switch to heater.
