- Heat pumps
- Pool heat pump
PO
Hayward PO on pool heat pump: open water temperature sensor
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
PO on square Hayward heat pumps (OP on round ones) means the water temperature sensor reads open. The usual culprit is a broken wire or the sensor itself; a technician measures it with the unit de-energised.
Safety first
Stop and check this first
- Hayward warns of high voltage at every terminal of the heat pump: with water nearby, only a qualified technician should open panels or measure the sensor.
- The R-410A refrigerant circuit is only for personnel who follow refrigerant handling regulations, as the guide points out.
Safe checks you can perform
- Identify the model and the display type
- Measure the real water temperature
- Switch the unit off and keep the panels closed
Leave these tasks to a qualified professional
- Do not attempt this professional task: Wiring check and sensor measurement
- Do not attempt this professional task: Board replacement only if the sensor tests good
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.
Wiring check and sensor measurement
What they doA technician looks for loose or broken wires to the board and measures the sensor with a meter, comparing it with the guide's 4.8k or 10k ohm chart.
They must show youthe measured resistance and the chart value for the water temperature.
In writingthe measured value, whether the wire was repaired or the sensor replaced, and the warranty.
Board replacement only if the sensor tests good
What they doIf the sensor reads the correct resistance and the wiring is fine, the guide says to replace the control board.
They must show youthe correct sensor reading that justifies changing the board.
In writingthe new board's part number, the cost and the warranty on the work.
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.
Identify the model and the display type
- Who:
- you, at the rating plate.
- How:
- write down the model from the rating plate and see whether your display shows PO (square models such as Summit or square HeatPro units) or OP (round models). The guide covers a specific list of model numbers on page 4 and each type uses a different sensor.
- Result that matters:
- giving the technician what they need to pick the right resistance chart.
- If your model is on the guide's list:
- mention it when you book the repair.
- If it is not listed:
- ask Hayward technical service for your model's documentation.
- Evidence to keep:
- a photo of the rating plate and one of the display showing the code.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
Measure the real water temperature
- Who:
- you, thermometer in hand.
- How:
- take the pool water temperature with a reliable thermometer and note it with the time. Hayward needs the real water temperature to compare the sensor's resistance against its chart.
- Result that matters:
- the technician can quickly decide whether the sensor reads right or wrong.
- If you have the reading:
- keep it for the visit.
- If you have no thermometer:
- the technician will measure it, but your reading speeds things up.
- Evidence to keep:
- the water temperature with date and time.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
Switch the unit off and keep the panels closed
- Who:
- you, at the control and breaker.
- How:
- turn the heat pump off at its control and, if you will wait several days for the technician, also switch off its circuit breaker. Hayward warns of 240 volts at all terminals and reserves service for trained personnel, so do not remove panels to look for the wire.
- Result that matters:
- nobody touches live wiring while you wait for service.
- If the filter pump runs on its own:
- filtration can carry on as usual.
- If you are unsure whether anything depends on the heat pump:
- ask your installer.
- Evidence to keep:
- the date you switched off and isolated the unit.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
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
- Hayward
- Product type
- Pool heat pump
Known code variants
- error PO bomba de calor piscina Hayward
- Hayward HeatPro OP
- Hayward HeatPro OP error
- Hayward open water sensor
- Hayward PO bomba de calor
- Hayward PO heat pump
- Hayward pool heat pump PO code
- Hayward Summit PO
- OP
- PO
- PO/OP
- sonda de agua abierta Hayward
What it means
Hayward's TSG-HTPMPa troubleshooting guide explains that PO, or OP on the display of round models, indicates an open water temperature sensor. Square models use a 4.8k ohm sensor and round models a 10k ohm one. The most common cause is the open sensor itself, but the guide says to check the wiring to the board first and measure resistance against the chart on page 31. PO alone does not prove which part has failed: if the sensor reads correctly, Hayward points to the control board.
Warnings and stop conditions
- Highsource verified
Hayward warns of high voltage at every terminal of the heat pump: with water nearby, only a qualified technician should open panels or measure the sensor.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
- Mediumsource verified
The R-410A refrigerant circuit is only for personnel who follow refrigerant handling regulations, as the guide points out.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
Symptoms and causes
Probable causes · in order
- Open water temperature sensorCommon
According to Hayward this is the most common cause: the sensor shows infinite or very high resistance for the real water temperature.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
- Loose or broken sensor wireCommon
The flow chart starts by looking for loose wires between the water sensor and the control board or interface board.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
- Faulty control boardLess common
If the sensor shows the correct resistance for the water temperature, the guide says to replace the control board.
Evidence: Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
Virtual technician
Does PO 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
Hayward/Summit Heat Pump Troubleshooting Guide (TSG-HTPMPa)
Hayward · 2018 · official_doc
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