Boiler Feed Pump Troubleshooting Guide

Symptom: Pump Won't Start

• Check power supply — verify all three phases are present (three-phase motors). A single-phasing motor will hum and trip on overload.
• Check motor overload — reset the overload relay. If it trips again, investigate the cause (bearing seizure, impeller jam, winding fault).
• Check the level controller — if the boiler water level is above the setpoint, the level controller won't call for feedwater. Verify the controller and its sensor.
• Check the starter — contactors can fail to close due to burned contacts or a failed coil.
• Check for mechanical seizure — try rotating the pump shaft by hand. If it won't turn, the pump is seized (bearing failure, impeller jam, or scale buildup).

Symptom: Pump Runs But Doesn't Deliver Water

• Air in the pump casing — the pump is air-bound. Vent the casing through the air release valve. Feed pumps on suction lift are particularly prone to this.
• Suction valve closed or blocked — verify the suction isolation valve is fully open and the strainer is not blocked.
• Check valve stuck closed — the discharge check valve may be stuck. Remove and inspect.
• Pump running backwards — on three-phase motors, if two phases are swapped, the motor runs in reverse. A backward-running centrifugal pump produces almost no flow. Swap two phases.
• Suction lift too high — if the water source is below the pump and the lift exceeds the NPSH available, the pump cavitates and delivers no flow. See our Pump NPSH guide.
• Worn impeller or wear rings — internal wear reduces pump capacity. If the pump is old, the impeller and wear rings may need replacement.

Symptom: Pump Cavitates

Cavitation sounds like gravel passing through the pump. It's caused by insufficient NPSH — the suction pressure is too low, causing the water to flash into vapour at the impeller eye.

• Check the deaerator level — low level in the deaerator reduces static head to the pump
• Check the deaerator pressure — if the deaerator pressure drops, the water temperature stays the same but the boiling point drops, causing flashing in the pump suction
• Check the suction strainer — a blocked strainer reduces suction pressure
• Verify the suction pipe is the correct size and as short as possible — undersized suction piping causes excessive friction loss
• Check for air leaks in the suction piping — air ingress reduces pump suction pressure
• If the water is near boiling (typical for deaerator-fed pumps), consider installing an inducer or a booster pump to increase NPSH

Symptom: Pump Vibrates

• Cavitation — see above. The most common cause of feed pump vibration.
• Misalignment between motor and pump — check coupling alignment with a dial indicator or laser aligner. Target: within 0.05mm.
• Worn bearings — listen with an ultrasonic stethoscope. A rough, grinding sound indicates bearing failure.
• Impeller imbalance — caused by uneven wear or erosion. Requires impeller replacement and rebalancing.
• Bent shaft — check runout with a dial indicator. Replace if out of tolerance.
• Resonance — the pump's natural frequency coincides with the operating speed or a piping vibration. May require a structural modification.
• Foundation looseness — check anchor bolts and grout. A loose foundation amplifies vibration.

Symptom: Pump Leaks at the Shaft Seal

• Mechanical seal failure — the most common cause. Check for cracks, worn faces, or damaged elastomers. Replace the seal.
• Packing gland too loose — if the pump uses packing (not a mechanical seal), tighten the gland nut slightly. A drip of 5–10 drops per minute is normal for packing.
• Shaft sleeve wear — grooves worn in the shaft sleeve under the seal cause leakage. Replace the sleeve.
• High seal water pressure — if the pump has an external seal flush, verify the pressure is within the seal's specifications.
• Misalignment — shaft misalignment causes the seal faces to run unevenly, accelerating wear. Realign the coupling.

Symptom: Motor Overload Trips

• Pump operating too far right on the curve (too much flow) — the motor is overloaded by excessive flow. Throttle the discharge valve or resize the impeller.
• High discharge pressure — if the boiler pressure is above the pump's rated head, the motor works harder. Verify the pump is sized for the actual operating pressure.
• Mechanical drag — worn bearings, a seized impeller, or shaft rub increase motor load. Check for free rotation by hand.
• Motor winding degradation — insulation breakdown causes increased current draw. Test with a megger.
• Voltage imbalance — if the three-phase supply has more than 2% voltage imbalance, the motor overheats. Check with a multimeter.