Turn the chiller off when flow stops. Start at the tub and follow the water path toward the return: water level, suction opening, valve, hose, strainer, pump, filter, chiller, treatment devices, and return fitting.
Flow-path checklist
| Check | What to look for |
|---|---|
| Water level | Suction fully submerged; no vortex pulling air. |
| Valves | Open and aligned with the intended path. |
| Hoses | No kink, collapse, frozen section, obstruction, or loose suction fitting. |
| Strainer/filter | Debris removed; cartridge correctly seated and serviceable. |
| Pump prime | Housing filled as directed; trapped air vented safely. |
| Direction | Arrows on pump, filter, chiller, and accessories agree. |
| Return | No closed valve, blocked fitting, or pinched hose. |
No flow after a filter change
Recheck the cartridge model, orientation, housing seal, air relief, and valve positions. A cartridge that is too restrictive or incorrectly fitted can starve the loop. Do not run indefinitely without a filter as a workaround.
No flow after draining
Air lock and loss of prime are common after service. Fill and vent the system using the documented sequence. Raising or lowering components, opening unions, or forcing water through a pump can damage equipment or create leaks if not authorized by the manual.
Stop conditions
Stop for a dry-running pump, hot motor, burning smell, repeated trips, damaged cable, water near electrical connections, cracked housing, or a leak that cannot be isolated.
Related guides and tools
- Chiller troubleshooting hub
- No-water-flow diagnostic
- Pump troubleshooting
- Chiller size calculator
- Water-volume calculator
Zero flow versus low flow
Zero flow often follows a closed valve, lost prime, air lock, blocked suction, disconnected pump, or major obstruction. Low flow more often points to a loading cartridge, dirty strainer, collapsing hose, excessive head, undersized plumbing, partial blockage, worn pump component, or suction-side air leak. Treat both as circulation faults and keep cooling disabled until the loop is stable.
How to prime the pump
There is no universal priming sequence. Some pumps are submersible, some are flooded-suction, and some can operate inline but are not self-priming. Danner’s FAQ states that trapped air in the volute can require priming. Use the pump manual: fill the housing or supply path as directed, open the required valves, vent at the approved point, and never allow extended dry operation.
Find a suction-side air leak
Persistent bubbles after initial purging can enter through a loose union, damaged O-ring, cracked hose, low water level, vortexing intake, or poorly sealed thread. A suction leak may draw air without leaking much water outward. Inspect dry and disconnected equipment; use only approved seals and lubricants.
Restriction test without bypassing safety
Service the strainer and filter first, then compare return flow. Do not remove protective screens or run unfiltered as a permanent solution. If the manufacturer permits a brief diagnostic configuration, follow it exactly and restore the system afterward. A filter that rapidly clogs is evidence of a contamination problem, not simply a reason to choose coarser media.
Head height and fittings
Pump maximum GPH is measured under specified conditions. Vertical rise, long narrow hose, elbows, tees, valves, filters, and the heat exchanger reduce operating flow. Danner explicitly notes that undersized tubing, fittings, transitions, and head height slow flow. Use a pump curve and system layout rather than the maximum-flow number.
After flow returns
- Confirm the return remains steady for several minutes.
- Inspect every fitting under operating pressure.
- Vent remaining air by the approved method.
- Check the filter housing and pump sound.
- Enable cooling and watch for a flow alarm or icing.
- Record what restored flow so the cause can be prevented.
References
Plunge: no water flow and Danner pump FAQ.
Flow restored but still low
Compare the system with a known clean baseline. A small return jet does not prove the chiller receives its required GPH. If the installation supports safe measurement, use an inline flow meter or timed-volume method on an appropriate open discharge. Never disconnect pressurized or energized plumbing for measurement. Compare the result with the chiller and filter limits.
Prevent the next outage
Label valve positions and flow direction, keep the correct spare cartridge, record the normal pump sound and return appearance, add a serviceable pre-strainer where approved, support hoses, and prime immediately after maintenance. If debris loads the filter unusually fast, solve the water-quality source instead of repeatedly increasing pump size.
Should the pump run continuously?
Use the schedule and duty rating for the exact pump, chiller, filter, and treatment system. Some pumps are continuous-duty; others are not. Danner explicitly labels certain utility pumps as not for continuous duty. A timer cannot make an unsuitable pump safe for a demanding loop.
Can a larger hose improve flow?
It can reduce friction when every fitting and device supports the size, but it will not correct a blocked intake, worn pump, air leak, closed valve, or excessive filter restriction. Redesign the complete loop rather than changing one connector.
