- Heat pumps
- Pool heat pump
LOW WATER FLOW
Pentair LOW WATER FLOW on pool heat pump: no water flow
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On the UltraTemp, LOW WATER FLOW means the pressure switch that senses water flow is open. Check that the filter pump is running, the filter is clean and the external bypass is closed.
Safety first
Stop and check this first
- Do not adjust the switch so the heat pump starts with low flow. Pentair warns that setting it too low can damage the appliance.
- Risk of electric shock: Pentair forbids internal adjustments by the user and asks for power to be turned off before any service.
Safe checks you can perform
- Filter pump running
- Filter, baskets and pump strainer
- External bypass and valves
- Recent changes to the installation
- Water pressure switch resistance
Leave these tasks to a qualified professional
- Do not attempt this professional task: Water pressure switch test and adjustment
- Do not attempt this professional task: System flow review
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Water pressure switch test and adjustment
What they doThe technician checks the switch resistance with flow; if the installation requires it, adjusts it with the wheel following Pentair's procedure or replaces it.
They must show youthe reading with flow and, after adjusting, the heat pump stopping as soon as the filter pump is switched off.
In writingwhether the switch was adjusted or replaced, the reference and the no-flow shutdown test.
System flow review
What they doThe technician checks filter, pump impeller, valves and suction air leaks, and confirms flow is above the 30 gpm [110 lpm] minimum.
They must show youthe measured flow, if there is a flow meter, and the state of the filter and valves.
In writingwhat was limiting flow and what was corrected.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Filter pump running
- Who:
- you, no tools.
- How:
- check the filter pump is running and that the timer or automation has it on; Pentair says the heat pump only runs with the pool pump on and water flowing.
- Result that matters:
- water flowing while you call for heat.
- If it was off and the alarm clears when it starts:
- it was a normal lack of flow.
- If the pump runs and the alarm stays:
- go to the filter.
- Evidence to keep:
- a photo of the display with the alarm and of the timer.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Filter, baskets and pump strainer
- Who:
- you.
- How:
- empty the skimmer baskets and the pump strainer basket and backwash or clean the filter following its instructions.
- Result that matters:
- more flow to the heat pump.
- If the alarm clears after cleaning:
- the filter or baskets were restricting flow.
- If the alarm stays with everything clean:
- go to the valves.
- Evidence to keep:
- the cleaning date and the filter gauge reading before and after, if it has one.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
External bypass and valves
- Who:
- you, no tools.
- How:
- check that the external bypass valve next to the heat pump is closed and the other valves are open or set so water passes through it.
- Result that matters:
- all the flow going through the heat pump.
- If the bypass was open and the alarm clears once closed:
- it was the bypass.
- If the valves were right:
- call the installer or a technician.
- Evidence to keep:
- a photo of the valve positions.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Recent changes to the installation
- Who:
- you.
- How:
- think whether the alarm started after the heat pump was installed or pipes were changed; Pentair says if the unit sits above water level, or the return is very short, the switch may need adjusting.
- Result that matters:
- knowing whether it is an installation setting problem.
- If it started after installation or pipework:
- ask the installer to review the switch setting.
- If the installation has not changed:
- the technician must test the switch.
- Evidence to keep:
- the installation or works date and photos of the pipework.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Water pressure switch resistance
- Who:
- an authorized service technician.
- How:
- with water flowing, check the resistance of the water pressure switch, located in the plumbing in the lower right corner of the unit.
- Result that matters:
- whether the switch closes with flow.
- If it is open with correct flow:
- Pentair says to replace it.
- If it closes correctly:
- the setting for the installation is reviewed.
- Evidence to keep:
- the reading taken with the pump running.
Panels must be removed from a mains powered unit next to water. Pentair forbids internal adjustments by the user: authorized technician only.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Heat pumps
- Brand
- Pentair
- Product type
- Pool heat pump
Known code variants
- alarma flujo de agua bomba de calor Pentair
- BAJO FLUJO
- LOW WATER FLOW
- Pentair bomba de calor piscina sin caudal
- Pentair heat pump low flow
- Pentair pool heat pump water flow alarm
- Pentair UltraTemp bajo flujo
- Pentair UltraTemp LOW WATER FLOW
- UltraTemp low water flow alarm
What it means
Pentair explains the LOW WATER FLOW alarm appears when the pressure switch sensing water flow is open. It is factory preset at 1.5 psi [10 kPa] and the UltraTemp needs a minimum flow of 30 gpm [110 lpm]. According to the troubleshooting table, causes are the circulation pump off, insufficient flow (dirty filters, clogged lint traps, valves, suction air leaks), an open external bypass or a bad pressure switch. Pentair also warns some installations require the switch to be adjusted. The alarm does not prove the switch is faulty: flow is almost always the cause.
Warnings and stop conditions
- Highsource verified
Do not adjust the switch so the heat pump starts with low flow. Pentair warns that setting it too low can damage the appliance.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
- Mediumsource verified
Risk of electric shock: Pentair forbids internal adjustments by the user and asks for power to be turned off before any service.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Symptoms and causes
Probable causes · in order
- Circulation pump offCommon
The filter pump is off or outside its schedule; the alarm shows as the pump stops and the heat pump restarts once flow returns.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
- Insufficient flowCommon
The pump runs, but dirty filters, clogged baskets or lint trap, a dirty impeller, wrong valve settings or suction air leaks reduce the flow.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
- External bypass openCommon
Water goes around the heat pump through the external bypass valve; the filter pump runs normally but the switch sees no pressure.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
- Switch not adjusted for the installationPossible
Pentair says if the heat pump sits above pool level or the return pipe is very short, the switch may need adjusting or an elbow fitting added.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
- Faulty water pressure switchPossible
With correct flow the switch stays open; Pentair asks for its resistance to be checked with water flowing and replaced if open.
Evidence: ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Virtual technician
Does LOW WATER FLOW still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
ULTRATEMP Heat Pump Installation and User's Guide (P/N 474099 Rev. AA)
Pentair · 2023 · official_doc
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