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Bosch 520HN Technical Service Bulletin page 2

Cleaning & replacing the pilot assembly
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1 2 | Cleaning & Replacing The Pilot Assembly
3. Clean orifice with compressed air or aerosol carburetor cleaner.
(NOTE: Do not ream or poke any object through orifice opening).
Reinstalling pilot assembly and orifice - 520HN Model
1. Screw clean or new orifice into pilot electrovalve and tighten with
8mm wrench. Do not over tighten.
2. Insert pilot assembly into burner and fit cylindrical air screen onto
orifice and pilot tube.
3. Insert screws through pilot shield and pilot assembly into burner
and tighten.
5. Replace cover, open gas supply and return heater to service.
6. If pilot flame is not strong and blue, replace orifice (NG is
stamped 2C, LP is stamped 1C).
Data subject to change without notice | Printed in the USA | BTC 746002316 A | 07.2010
Technical Service Bulletin
Bosch Thermotechnology Corp.
50 Wentworth Avenue
Londonderry, NH 03053
Tel: 1-866-642-3198
Fax: 1-603-584-1687
Bosch Thermotechnology Corp.



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