Troubleshooting, Maintenance, Schedule – Xylem MM 226C Series 69 Low Water Cut-Offs For Steam Boilers User Manual

Page 8: Procedure, Caution

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.

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.

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.

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.

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.