Bosch 520HN Reference manual

Technical Service Bulletin:
Removing & Cleaning The Burners
Models: 520HN, 520PN, 330PN
LP & NG are extremely flammable. Take extra
precautions when performing any work to the heater.
WARNING
Removing pilot assembly
Models: 520PN, 330PN (Fig. 1):
1. Shut off gas and water to heater, then remove front cover.
2. Remove wire clip holding top of pilot tube into bracket.
3. Move lower end of pilot tube to left to release from black clip
on gas valve. Be sure to catch air screen attached to base of
pilot tube.
4. Pull upwards on upper end of pilot tube to release from bracket.
5. Remove black clip from bracket to release spark electrode.
6. Gently press down on top of thermocouple to release it from
bracket.
Figure 1
Pilot air screen
Pilot wire clip
Burners
Pilot tube
Thermocouple
lead
Models: 520HN (Fig. 2):
1. Shut off gas and water to heater, then remove front cover.
2. Remove both pilot bracket screws and pilot shield from front of
burners.
3. Remove pilot assembly from burner bracket. Be sure to catch air
screen secured to base of pilot assembly.
Figure 2
Pilot shield
Pilot bracket
screws
Burners
Pilot air
screen
Pilot air
screen
Burner set
screws
Removing the burners
1. Remove 2 burner set screws on the right side of the gas valve.
(Fig. 2)
2. Remove four screws from both right and left burner brackets
and set aside. (Fig. 3)
3. Push entire burner assembly up to seperate from the gas valve.
4. Tilt right side of burners up and slide them out at an angle to the
left. (Fig. 4)
Figure 3

12 | Removing & Cleaning The Burners Technical Service Bulletin
Data subject to change without notice | Printed in the USA | BTC 746002313 A | 07.2010 Bosch Thermotechnology Corp.
Bosch Thermotechnology Corp.
50 Wentworth Avenue
Londonderry, NH 03053
Tel: [phone]
Fax: [phone]
www.boschpro.com
Figure 4
Cleaning the burners (Fig. 5)
1. Use a soft wire brush across burner ns to loosen any debris
and then vacuum out.
2. Check to see that the 18 brass gas injectors in the rear of the
burner assembly are clean. To access, remove 8 Philips head
screws to the left and right of the two center brass Philips head
screws at the rear of the burner. The burners should separate
into two halves exposing injectors. Blow clean with compressed
air or carburetor cleaner and wipe dry with cloth. Do NOT poke
injectors or at tempt to clean with drill bits, wires or other
objects. Clean rear venturi passages with a pipe cleaner and
soapy water. Rinse clean and let dry before reinstalling. Follow
instructions in reverse to reconnect burner halves.
Burners disassembled
Burner fins
Burner
venturi
passage
Gas injectors
B
B
u
r
ne
rs
di
s
i
i
a
ss
e
m
ble
d
B
B
urne
r
f
ins
B
urne
r
v
entur
i
p g
p
a
s
s
a
g
e
G
as
injector
s
r
r
Figure 5
Reinstalling the burners
1. Reinstall burners into burner area.
2. Reinstall set screws on right side of gas valve and tighten.
3. Reinstall right and left burner brackets with the four screws. The
brass screws attach to frame.
Reinstalling pilot assembly
Models: 520PN, 330PN (Fig. 1):
1. Reinsert thermocouple and snap into place. Thermocouple tip
should sit 1/4” above the burner bed.
2. Put spark electrode into place and attach with clip.
3. Slide upper end of pilot tube into bracket on burner assembly
and reinsert pin.
4. Slide base of pilot tube to the right into clip. Ensure pilot air screen
is installed between pilot tube and pilot orice.
Models: 520HN (Fig. 2):
1. Slide pilot air screen over pilot tube.
2. Slide pilot assembly into place. Reinsert pilot shield and secure
with screws to the burner assembly.
Returning heater to service
Models 520PN. 330PN:
1. Turn on gas and light pilot. Test for possible gas leaks where
burners connect to the gas valve.
Models 520HN:
1. Turn on gas and check for leaks where the burners connect to
gas valve by applying leak detecting solution as you initiate
water ow to activate the heater. Allow enough time to bleed all
air in gas line. Bubbles are a sign of a leak.
All models:
2. If there are bubbles at either connection immediately shut off
water and gas. Loosen the burner set screws on the right side of
gas valve. Remove the burners and inspect the o-ring. Replace if
damaged. Reseat burners and tighten set screws. Check again
for leaks.
3. Replace front cover when complete.