Pump, close — Inzonex Modular Insulation, hot-water skid
Pumps / Faults
Circulation pump faults
A pump that is running is not necessarily pumping.
Most pump call-outs are one of four complaints. Nothing is circulating, it is making a noise, it is leaking, or it keeps tripping. Each has a short list of causes. Each is diagnosed at the pump with what is already there: a gauge either side, the isolating valves, and the arrow on the casing.
No flow
Running but not circulating
Air in the casing
The commonest cause by a distance, and the one that makes a glandless pump sound different rather than louder. Open the vent on the pump and let the air out. On a wet rotor that water also cools the bearings, so an airlocked pump left running is a damaged pump.
A valve that is shut
A valve closed for work and not reopened, or a commissioning valve set to almost nothing. The isolating valves either side of the pump are the first thing checked, before anything is dismantled.
Running backwards
A three-phase pump wired in the wrong phase rotation runs backwards. It still moves a little water, so it does not look obviously wrong. The arrow on the casing and the direction indicator settle it in seconds.
Seized after standing
A pump left stopped for a long period can stick. It is why standby pumps are exercised on a schedule rather than left for the day they are needed.
Noise
What the sound means
Air, again
Gurgling or a rushing sound is air passing through. It clears when the system is vented and it comes back if the fill or the vent arrangement is letting air in.
Cavitation
A harder rattling, like gravel in the casing, from insufficient pressure at the suction. It is a system fault rather than a pump fault: static pressure, a blocked strainer, or a suction line that is too restrictive. It erodes the impeller while it goes on.
Bearings
A steady whine or rumble that rises with speed. On a glandless pump the bearings sit in the pumped water, so their condition follows water quality. Treat the system, not just the pump.
Leaks and trips
The other two complaints
Mechanical seal
On a glanded pump a weep at the shaft is the seal, and a seal that has started weeping does not recover. A glandless pump has no such leak path. A wet patch under one is coming from a flange or the casing.
At the flanges
Ordinary flanged joints with ordinary gaskets, and treated as such - re-torqued warm, gasket replaced if it has aged.
Tripping
A pump drawing more current than it should is doing more work than it should. That means a blocked impeller, a bearing on the way out, or a system resistance that has changed. Resetting it repeatedly is not a diagnosis.
What insulation has to do with it
Keeping the pump workable
The terminal box and the nameplate stay clear
Every check above needs the arrow, the nameplate or the terminal box. A cover over any of them is a cover that gets cut off during the first fault, and after that the casing runs bare permanently.
So does the drain
The casing drain and the vent are left outside the module so the pump can be vented and drained without touching the insulation.
Reference
Symptom against first check
| Symptom | Usual cause | What to check first |
|---|---|---|
| Running, nothing circulating | Air in the casing, or a shut valve | Vent the pump, then the isolating valves |
| Gurgling or rushing | Air passing through | Vent, then look at the fill |
| Rattling, like gravel | Cavitation at the suction | Static pressure and the strainer |
| Steady whine that rises with speed | Bearings | Water quality and running hours |
| Weeping at the shaft | Mechanical seal, on a glanded pump | Seal replacement, not adjustment |
| Tripping the overload | Blocked impeller or changed system resistance | Current against the nameplate |
Symptom · Usual cause · What to check first
Asked about circulation pump faults
Questions.
Answers distinguish modelled heat-loss estimates from equipment selection and service guidance.
Why is my circulation pump running but not circulating?
Air in the casing is the commonest cause, followed by a valve left shut after work. Vent the pump first, then check the isolating valves either side. On a three-phase pump, check it turns the way the arrow on the casing says. Reversed rotation still moves a little water and does not look wrong.
Why is my pump making a noise?
Gurgling or rushing is air, and it clears when the system is vented. A hard rattle like gravel is cavitation, meaning not enough pressure at the suction. That usually comes from static pressure, a blocked strainer or a restricted suction line, and it damages the impeller while it continues. A steady whine that rises with speed is bearings.
Where does a circulation pump leak from?
On a glanded pump, the mechanical seal on the shaft, and once it has started it does not recover. A glandless pump has no shaft seal at all, so a wet patch under one is coming from a flanged joint or the casing itself.
Why does my pump keep tripping?
It is drawing more current than the overload allows, so it is doing more work than it should. That means a blocked or damaged impeller, a failing bearing, or a change in system resistance. Compare the running current with the nameplate before resetting it again.
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The node page carries the heat-loss figures and the size table.