- Heat pumps
- Air-to-water heat pump
P1
Baxi P1 on an HP40/HP50 heat pump: high pressure switch protection
Risk level
High
Professional inspection is recommended.
Urgency
Medium
Quick answer
On Baxi HP40 and HP50 heat pumps, P1 means the refrigerant high pressure switch has tripped. Check the water pressure: if it is below 1 bar, ask the installer to refill it. Do not touch the refrigerant circuit.
Safety first
Stop and check this first
- Baxi states that the refrigerant in the unit is flammable and toxic and that only an F-gas qualified technician can carry out a full leak test. If you smell gas or suspect a leak, turn off combustion appliances, ventilate and do not use the unit until a qualified installer has repaired it.
Safe checks you can perform
- Water pressure on the gauge
- Operating mode and outdoor unit
- Purging, flow and refrigerant circuit
Leave these tasks to a qualified professional
- Do not attempt this professional task: Rule out the water side before the refrigerant
- Do not attempt this professional task: Refrigerant charge and expansion valve
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.
Rule out the water side before the refrigerant
What they doThe technician checks pressure, air and water flow before touching the refrigerant charge or the expansion valve.
They must show youthe water pressure between 1.5 and 2 bar after refilling and the purge done.
In writingthe cause found and what was corrected.
Refrigerant charge and expansion valve
What they doIf the water side is fine, the certified technician checks the electronic expansion valve, its connector and the refrigerant charge.
They must show youthe refrigerant amount removed or charged against the rating plate.
In writingtheir F-gas certificate number, the amount and the leak test.
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.
Water pressure on the gauge
- Who:
- you.
- How:
- read the water circuit pressure gauge.
- Result that matters:
- Baxi says to refill if it is below 1 bar, to between 1.5 and 2 bar.
- If it is below 1 bar:
- it is a cause Baxi gives for P1; ask the installer to refill and find the loss.
- If it is between 1.5 and 2 bar:
- low pressure is ruled out; flow, air or the refrigerant circuit remain.
- Evidence to keep:
- a photo of the gauge with the date.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
Operating mode and outdoor unit
- Who:
- you, from outside and without opening anything.
- How:
- note whether the code came while heating, making hot water or cooling, and look whether the outdoor exchanger is covered by dirt or objects.
- Result that matters:
- in cooling Baxi points at a dirty or blocked exchanger; in heating, at the water side.
- If it came while cooling and there is a visible blockage:
- clear it from outside and ask the installer to clean the exchanger.
- If it came while heating:
- the water side or the refrigerant are the suspects; it is not an outdoor blockage.
- Evidence to keep:
- a note of the mode and a photo of the outdoor unit.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
Purging, flow and refrigerant circuit
- Who:
- an F-gas certified technician.
- How:
- they purge air, check the water flow and, if the water side is fine, check the electronic expansion valve, its connector and the refrigerant charge.
- Result that matters:
- whether flow is correct and whether the refrigerant charge matches the rating plate.
- If there was air or low flow:
- a hydraulic cause is confirmed and the refrigerant is ruled out.
- If the water side is fine and the charge is too high or the valve is locked:
- a refrigerant circuit cause is confirmed.
- Evidence to keep:
- a report with the measured charge and the valve condition.
Flammable and toxic R32 refrigerant and live parts. Only an F-gas certified technician may work on the circuit.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
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
- Baxi
- Product type
- Air-to-water heat pump
Known code variants
- Baxi heat pump P1
- Baxi HP40 P1
- Baxi HP50 P1
- Mitsubishi P1
- Mr. Slim P1
- PKA P1
What it means
Baxi defines P1 as high pressure switch protection. In heating and hot water it links it to low water flow, high water temperature or air in the system, water pressure below 1 bar, refrigerant overcharge and an electronic expansion valve that is locked or has a loose connector. In cooling, to a heat exchanger cover left on or a dirty exchanger. The code does not prove the compressor or the switch is faulty.
Warnings and stop conditions
- Highsource verified
Baxi states that the refrigerant in the unit is flammable and toxic and that only an F-gas qualified technician can carry out a full leak test. If you smell gas or suspect a leak, turn off combustion appliances, ventilate and do not use the unit until a qualified installer has repaired it.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
Symptoms and causes
Probable causes · in order
- Low water flow or airCommon
In heating, if the water does not carry the heat away, refrigerant pressure rises. It goes with air in the circuit or very hot water.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
- Water pressure below 1 barCommon
Baxi asks to refill to 1.5 to 2 bar. It shows on the gauge without opening anything.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
- Refrigerant overcharge or expansion valvePossible
Too much refrigerant or a locked electronic expansion valve give P1 with a correct water circuit. Only an F-gas technician can check it.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
- Dirty outdoor exchanger in coolingPossible
In cooling mode, Baxi points at a dirty or blocked exchanger or a cover not removed.
Evidence: Baxi HP40/HP50 monobloc air to water heat pump, installation and service manual 784570
Virtual technician
Does P1 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
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