Xylem MM 226C Series 69 Low Water Cut-Offs For Steam Boilers - Manual (Page 8)

Xylem Inc.
8200 N. Austin Avenue
Morton Grove, Illinois 60053
Phone: (847) 966-3700
Fax: (847) 965-8379
www.xyleminc.com/brands/mcdonnellmiller
McDonnell & Miller is a trademark of Xylem Inc. or one of its subsidiaries.
TROUBLESHOOTING
Problem:
1. Burner does not shut off on low water.
a.
Cause: Float shield is loaded with mud or sedi-
ment. Shield may be out of position or
damaged; bellows folds obstructed.
Test: With water level below the control check if
terminals 1 and 2 are open. If not, remove
switch and manually test if terminals 1 and
2 can be opened.
Solution: Remove the control and clean. At this time,
check for a build-up of scale or sediment
between corrugations of the bellows.
b.
Cause: Contacts are fused together.
Test: Remove switch and operate manually to ver-
ify proper switch operation.
Solution: Replace switch. Check electrical load and
make sure it is within the ratings of the
switch.
2. Electric water feeder does not shut off.
a.
Cause: Float obstructed or damaged. Build-up of
scale or sediment between corrugations of
the bellows. Shield may be out of position.
Test: With water level above the control, check if
terminals 3 and 4 are open. If not, remove
switch and manually test to verify termi-
nals 3 and 4 can be opened.
Solution: Check the clearance of the shield; replace
or clean the bellows.
b.
Cause: Contacts are fused together.
Test: Remove switch and operate manually to
verify proper switch operation.
Solution: Replace switch. Check electrical load and
make sure it is within the ratings of the
switch.
MAINTENANCE
SCHEDULE:
• Blow down weekly (at least once) when the
boiler is in operation.
• Disassemble and inspect annually. Replace
the low water cut-off if it is worn, corroded,
or if components no longer operate properly.
• Inspect the shield, float and bellows annually.
Remove all sediment and debris.
• We recommend replacement when the switch no
longer operates properly.
If you choose to replace the switch, order the
McDonnell & Miller replacement switch and follow the
Repair Procedure provided.
• Replace the low water cut-off every 10 years.
More frequent replacement may be required when
severe conditions exist such as rapid switch cycling,
surging water levels, and use of water treatment
chemicals.
PROCEDURE:
Test the low water cut-off when the water level is at its
normal level and the burner is on.
Slowly open the
boiler drain valve and observe the water level fall in
the gauge glass. Close the valve after verifying that
the alarm/feeder contacts have closed and the burner
shuts off. If this does not happen, immediately shut off
the boiler and correct the problem.
! CAUTION
To prevent serious personal injury from steam pipe
blow down, connect a drain pipe to avoid exposure to
steam discharge.
Failure to follow this caution could cause personal
injury.
© 2013 Xylem Inc. MM-226C July 2013 Part No. 246753