24
High Limit Removal
1. Disconnect top portion of unit. (See Heat
Exchanger Removal procedure, steps 1 thru 7 and
step 10.)
2. Remove defective high limit and replace with new
high limit.
3. Reverse above procedure to reinstall.
Pilot Safety
Millivolt Units
The heaters equipped with the standing pilot (millivolt
system) have pilot generators which act as a safety
device to shut-off the flow of gas to the main burners
and the pilot burner in case the pilot flame is extin-
guished. The pilot burner must be manually relighted
to place the heater in operation again. Refer to the
lighting instructions provided on the heater label.
IID Units
The heater employs a pilot safety which closes the
main gas valve within 8/10ths of a second whenever
the pilot flame is interrupted. Pilot flame is automatical-
ly lit when the device is powered. Unit performs its own
safety check and opens the main valve only after the
pilot is proven to be lit.
Burner Tray Removal
1. Shut-off main electrical power switch to heater.
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.
6. Disconnect wires that terminate at gas valve, and
thermal fuse.
7. Slide out burner tray.
8. Reverse above procedure to reinstall.
Gas Valve Removal
1. Remove burner tray. (See Burner Tray Removal
procedure).
2. Disconnect pilot tubing from gas valve.
3. Remove gas valve with manifold from burner tray.
4. Remove manifold from gas valve.
5. Reverse above procedure to reinstall.
NOTE:
An erratic high limit is often characteristic of
internal heat exchanger problem, e.g. scale build-up,
U.G. operation. Refer to Troubleshooting section.
Main Burner and Orifice Removal
1. Remove burner tray. (See Burner Tray Removal
procedure).
2. Remove screws and burner hold-down bracket.
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 over-tighten when reinstalling.
Pilot Removal and Cleaning
1. Remove burner tray. (See Burner Tray Removal
procedure).
2. Disconnect pilot tubing, disconnect wires from gas
valve (millivolt unit only).
3. Disconnect pilot bracket from burner shield.
4. Remove pilot from bracket.
5. Remove pilot orifice and air opening (Honeywell
MILLIVOLT unit only), and clean with wire or small
brush. CAUTION! DO NOT enlarge hole in pilot
orifice.
6. Reverse above procedure to reinstall.
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.
t
o
li
P
Air
Opening
Orifice
Fig. 28: Honeywell Pilot
