IM 907 / Page 19 of 24
Service Diagnosis
Fails to Maintain Temperature
1. Undersized unit heater, boiler, pump or piping.
2. Excessive exhaust air (exhaust fans may have
been added since heating installed).
3. Unit heater operating at lower speed when sized to
operate at high speed.
4. Unit heater mounted too high - heated air not
deliveredtooorlevel.
5. Thermostat - improper location or setting, or not
functioning.
6.
Dirty or clogged coil.
Unit Blows Cold Air
1.
Manual shut-off valve closed.
2. Insufcientsteampressureoflackofhotwater.
3. Aquastat not functioning.
4. Improper venting.
5. Steam trap not functioning.
6. Drip leg too short (steam system).
7. Return line plugged (steam system).
8. Pump undersized or not operating (hot water
system).
Does Not Operate When Heat Needed
1.
Defective motor or electrical connections.
2. Thermostat, aquastat or pressure limit control not
functioning.
Fails to Deliver Heat to Floor
1.
Units mounted too high.
2. Operating on low speed.
3. Final air temperature too high.
4. Louvers not adjusted properly.
5. Wrong type of diffuser (on verticals).
6. Undersizedunitheater(insufcientairdelivery).
7. Wrong type of unit (may require vertical delivery).
8. Cross ventilation or drafts.
9. Obstructionstoairow.
Noisy Unit
1.
Loose bolts or screws.
2. Fan blade bent, out of balance.
3. Dirt accumulation on fan blades.
4. Fan hub or blade rivets loose.
5. Motor shaft thrust bearing worn.
6. Motor mounting bent, fan not positioned properly in
venturi.
7. Unit mounted too rigidly, transmits vibration noise.
8. Conduit too rigid, transmits vibration noise.
9. BX cable touching unit heater, chatters as casing
vibrates.
Unit Leaks
1.
Loose connection.
2. Internal corrosion.
Employees Complain of Hot Blast
1.
Air stream aimed directly at employees.
2. Louvers not adjusted properly.
3. Wrong type of diffuser (on verticals).
4. Excessivenalairtemperature.
Unit Operates Too Long
1.
Thermostat installed on cold wall or otherwise
improperly located.
2. Heavy exhaust fan load. (May have been increased
since heating system was laid out).
3. Aquastat or pressure limit control not functioning
properly.
4. Unit is undersized.
Frequent Motor Failure
1.
Voltageuctuationstoohighortoolow.
2. Excessiveorinsufcientlubrication.
3. Wiring to motor undersized.
4. Improper electrical connections.
5. Motor operating in too high air temperature.
6. Restrictedairowthroughunitduetocloggedcoil,
closed louvers, too much duct work connected to
unit.
7. Fan out of balance.
8. Unbalanced voltage on 3 phase power.
Premature Failure
1.
Severe internal corrosion due to condition of boiler
water.
Coil Failure
1.
Severe internal corrosion from feedwater.
2. Type of boiler treatment.
3. Entrained air causing water hammer.
4. Too much outdoor air portion in freezing
temperatures.
5. Continuous operation above 150 PSI (375°F) (steam
systems).