Troubleshooting Checklist; Not Enough Or No Hot Water; Water Is Too Hot; Boiler Makes Strange Sounds - A.O. Smith NW 37-670 Instruction Manual

Lime scale should be removed from the elements by dissolving the
accumulation in UN•LIME® delimer. UN•LIME is a non-muriatic
delimer, available through your dealer or distributor. Do not use
muratic or hydrochloric acid base deliming solutions to remove lime
scale from the elements. Do not pour delimer into tank.
All models:
1. Turn off electrical disconnect switch.
2. Drain the boiler following DRAINING instructions.
3. Remove the cabinet panel which covers the heating elements.
• Remove insulation as necessary to reach the element area.
4. Remove the bolts from each element and remove the elements
from the opening.
• Disconnect element wiring as necessary.
• Use a twisting, pulling action to remove elements scaled beyond
the size of the tank opening.
• Brush loose scale from elements.
• Silicates, sulfates and aluminates must be removed by scraping or
other mechanical means. Lime scale dissolvents will not remove
these types of scale which are occasionally encountered.
5. Lime scale removal:
Before calling for service, check the following points to see if the
cause of trouble can be identified and corrected. Reviewing this
checklist may eliminate the need of a service call and quickly restore
the boiler to service. The illustration on page 5 identifies the location
of most of the boiler components.
BE SURE TO TURN OFF THE ELECTRICITY WHEN CHECKING
EQUIPMENT.

not enough or no hot water

1. Be certain the electrical disconnect switch serving the boiler is in the
ON position. The pilot switch(es) on the cabinet front should be on.
• In some installations the boiler electrical service may be limited
by the power company or boiler controls. If the boiler operates
on a controlled circuit heat may be effected.
2. Check the fuses.
• The electrical disconnect switch usually contains fuses.
• The boiler has fuses located behind the cabinet door, see page
5 for location.
3. If the water was excessively hot, and is now cold, the high
temperature cutoff may have operated (manual reset equipped
models).
• To reset, turn off electricity and remove the back panel and push
the reset button.
• Repeated operation of the high temperature cutoff should be
investigated by your servicer.
4. The capacity of the boiler may have been exceeded by a large
demand for heat.
• Large demands require a recovery period to restore water
temperature.
5. Sediment or lime scale may be affecting boiler operation. Refer to
MAINTENANCE for details.

water is too hot

1. Refer to TEMPERATURE REGULATION.
Boiler makes sounds
1. Sediment or lime scale accumulation on the elements may cause
6. Flush cleaned ends of elements with water when deliming or
7. Remove sediment and scale from the tank bottom through the
8. Clean remaining gasket material from tank and element flanges. Do
9. Replace elements as follows:
10. Connect element wiring as necessary.
11. Follow FILLING instructions to restore boiler to service.

trouBleshootInG checklIst

2. Some of the electrical components of the boiler make sounds
water leakage is suspected
1. Check to see if the drain valve is tightly closed.
2. If the outlet of the relief valve is leaking it may represent:
3. Examine the flange area of the elements and tank cleanout for
systeM water test
system water test
Review SYSTEM CLEANING section, for a description of six problems
which result from loss of system chemical stability. Chemical stability
is checked by:
1. Draw off water from system. Is it dirty, discolored or odorous?
2. What is the pH of the system water? It should be neutral or slightly
3. Does "air" purged from system vents burn? If so, the "air" is
If any of the above conditions are present, all waterways should be
cleaned and the water adjusted to an alkaline condition.
If you cannot identify or correct the source of malfunction:
1. Place the boiler electrical disconnect switch in the OFF position.
2. Close the make-up water inlet valve to the boiler.
3. Contact your servicer.
18
• Place limed ends of heating elements into UN•LIME delimer
and allow scale to dissolve. Do not permit delimer or water to
contact heating element electrical terminals.
cleaning is completed.
tank cleanout.
• The make-up water valve and boiler drain valve may be opened
to flush during the cleanout process.
not reuse original element gasket. The element gasket is Part No.
5109.
• Put a new gasket on each element.
• Install into tank opening.
• Uniformly tighten element bolts. Torque to approximately 32 ft /lbs.
• Check for water leaks around elements and proper
operation when boiler is filled.
• Replace insulation and cabinet panel.
sizzling and hissing noises when the boiler is operating.
• The sounds are normal , however, the tank bottom and elements
should be cleaned. Refer to MAINTENANCE for details.
which are normal.
• Contactors will "click" or snap as the boiler starts and stops.
• Transformers and contactors often hum.
• Excessive water pressure or air in the system.
• Faulty relief valve.
gasket leakage.
• Tighten the bolts or, if necessary, follow the WATER AND LIME
SCALE REMOVAL procedure to replace the gaskets.
alkaline.
actually gas.