Boiler water circulating pump motors are critical equipment. Any repair must be done systematically to avoid repeat failures and boiler trips.
1. Common Motor Problems
✔ Motor not starting
✔ High current / tripping
✔ Overheating
✔ Abnormal noise / vibration
✔ Low insulation resistance
✔ Bearing failure
✔ Moisture ingress
2. Step-by-Step Repair Procedure
A. Initial Inspection (At Site / Workshop)
☐ Record nameplate details (kW, V, A, RPM, Insulation class)
☐ Check external damage & terminal box
☐ Measure IR (Phase–Phase & Phase–Earth)
☐ Measure winding resistance balance
☐ Check earthing
☐ Inspect coupling & alignment
B. Electrical Fault Repair
1. Low IR / Earth Fault
- Dry motor in oven or by space heater
- Clean winding surface
- Re-varnish if insulation is weak
2. Phase to Phase Fault
- Rewinding mandatory
- Upgrade insulation to Class H
- Improve end winding bracing
3. High Current / Unbalance
- Check supply voltage unbalance
- Inspect winding symmetry
- Verify correct Star/Delta connection
C. Mechanical Repair
Bearing Failure
☐ Replace bearings (recommended for boiler pumps)
☐ Check bearing housing wear
☐ Use high-temperature grease
☐ Maintain correct axial clearance
Vibration / Noise
☐ Rotor dynamic balancing
☐ Shaft run-out check
☐ Proper alignment with pump
☐ Check fan & cooling ducts
D. Rewinding Repair (If Required)
☐ Record original winding data
☐ Controlled stripping (≤ 350°C)
☐ Use Class F/H insulation materials
☐ Tight end-winding lacing
☐ VPI or double dip–bake impregnation
☐ HV, IR, PI testing after rewinding
3. Post-Repair Testing Checklist
☐ IR value satisfactory
☐ PI value ≥ acceptable limit
☐ HV test passed
☐ No-load current within limit
☐ Temperature rise normal
☐ No abnormal noise or vibration
4. Common Causes of Repeated Failures
❌ Poor alignment
❌ Boiler water leakage on motor
❌ Poor ventilation
❌ Inferior rewinding materials
❌ Running pump in cavitation
❌ Continuous overload
5. Preventive Actions (Highly Recommended)
✔ Install RTD/PTC temperature sensors
✔ Regular IR testing
✔ Maintain pump alignment
✔ Ensure proper ventilation
✔ Upgrade insulation during rewinding
✔ Avoid dry running
6. When to Repair vs Replace?
| Condition | Action |
|---|---|
| Minor insulation issue | Repair |
| Bearing failure only | Repair |
| Burnt winding | Rewind |
| Core damage | Replace motor |
| Multiple rewinds | Replace |
⭐ Expert Tip
For boiler circulating pumps, motor failure = boiler shutdown.
Always prioritize quality repair over cost saving.