Bosch Therm 520HN Technical Service Bulletin

Technical Service Bulletin:
Removing & Cleaning The Burners
Models: 520HN, 520PN, 330PN
WARNING
LP & NG are extremely flammable. Take extra
precautions when performing any work to the heater.
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.
Pilot wire clip
Pilot tube
Burners
Thermocouple
lead
Pilot air screen
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.
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)
Figure 1
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 2
Figure 3