- Heat pumps
- Air-to-water heat pump
F788
Saunier Duval F.788 on a heat pump: heating circuit pump fault
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Medium
Quick answer
F.788 warns that the tower circulating pump has locked itself out after an internal fault such as dry running or abnormal voltage. Check the pressure on the display and the house power supply, bleed radiators if there is air, then call the installer.
Safety first
Stop and check this first
- Do not open the tower to reach the pump or the board. Before any electrical work, the installer isolates all poles and waits at least 3 minutes for the capacitors to discharge.
Safe checks you can perform
- Check the pressure the GeniaSet shows
- House power supply switched on
- Bleed radiators if you notice air
- Look at the status codes
Leave these tasks to a qualified professional
- Do not attempt this professional task: 30 second power cut and connector check
- Do not attempt this professional task: Circuit purge and strainer cleaning
- Do not attempt this professional task: Pump test before replacement
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.
30 second power cut and connector check
What they doThe installer removes power from the heat pump for at least 30 seconds, as the fault table requires, and checks the pump plug contact on the board.
They must show youthe state of the connector and the pump starting after the cut.
In writingwhether the connector was loose or damaged and what was fixed.
Circuit purge and strainer cleaning
What they doThe technician bleeds air from the building circuit and cleans the dirt strainers that restrict the water flow.
They must show youthe measured flow rate against the manufacturer minimum and the strainers after cleaning.
In writingwhat was purged, the strainer condition and the resulting flow.
Pump test before replacement
What they doOnly if the fault persists with water, pressure and connections in order does the professional test the pump and decide whether it must be replaced.
They must show youthe supply voltage measured at the pump and the fault history.
In writingthe test result, any replacement pump with its part number and the reason.
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.
Check the pressure the GeniaSet shows
- Who:
- you, from the tower display.
- How:
- read the filling pressure shown by the GeniaSet. Below 0.07 MPa (0.70 bar) the system is short of water and the pump can end up running dry.
- Result that matters:
- a pressure of at least 0.7 bar.
- If it is lower:
- ask your authorised professional to top up and find out why water is being lost.
- If it is fine:
- carry on with the power supply.
- Evidence to keep:
- photo of the display with F.788 and the pressure shown.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
House power supply switched on
- Who:
- you, at the fuse box of your home.
- How:
- see whether any fuse or breaker feeding the heat pump has dropped. The troubleshooting table in the operating manual says to reconnect the building power supply when the appliance is not working.
- Result that matters:
- every protective device for the system in its on position.
- If a breaker had dropped:
- put it back up one time only; should it drop again, leave it down and ring the installer.
- If everything was on:
- go on to check for air.
- Evidence to keep:
- photo of the consumer unit and of the switch that was down, if any.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
Bleed radiators if you notice air
- Who:
- you, with a radiator bleed key.
- How:
- if radiators are cold at the top or you hear gurgling, bleed them as the operating manual troubleshooting table suggests. Look at the pressure again afterwards, since bleeding lowers it.
- Result that matters:
- radiators free of air and pressure still in the correct range.
- If air came out:
- note it for the technician, as air can leave the pump running dry.
- If there was no air or the problem repeats:
- contact the authorised professional.
- Evidence to keep:
- which radiators had air and the pressure before and after bleeding.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
Look at the status codes
- Who:
- you, from the Live Monitor.
- How:
- press the two keys the manual names at the same time to open the current status code and write down what appears; S.277 means the building circuit pump has stopped and is waiting to restart.
- Result that matters:
- knowing whether the unit was still in its restart sequence before locking out.
- If S.277 shows:
- let the sequence finish without switching off again and again.
- If only F.788 stays on:
- tell the installer, quoting the code you noted.
- Evidence to keep:
- photo of the status code on the Live Monitor.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
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
- Saunier Duval
- Product type
- Air-to-water heat pump
Known code variants
- aroTHERM F.788
- aroTHERM plus F788
- bomba circulación F.788
- circulating pump F.788
- error F.788 aerotermia Saunier Duval
- F788
- Genia Air F.788
- Genia Air Max F788
- GeniaSet F.788
- Saunier Duval F788
- Saunier Duval heat pump F.788
- Vaillant F788
What it means
In the GeniaSet tower of a Genia Air Max, the electronics of the high-efficiency building circuit pump detect a problem (dry running, blockage, overvoltage or undervoltage), switch the pump off and lock it. When the pump is not running, the heat pump stops for 10 minutes and tries again; after the third failed restart it shows F.788. The message does not by itself prove the pump needs replacing, because air or dirt in the circuit can cause it too. Details come from the Spanish Saunier Duval manual.
Warnings and stop conditions
- Mediumeditorial warning
Do not open the tower to reach the pump or the board. Before any electrical work, the installer isolates all poles and waits at least 3 minutes for the capacitors to discharge.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
Symptoms and causes
Probable causes · in order
- Dry running from air or low waterCommon
The pump itself logs dry running, and the manufacturer lists purging the building circuit among the fixes for this code.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
- Pump held back by dirtPossible
A mechanical blockage is another listed reason, and the table asks for the dirt strainers to be checked for free passage.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
- Overvoltage or undervoltage at the pumpPossible
The pump electronics also lock out when they see overvoltage or undervoltage on their supply.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
- Poor plug contact on the boardLess common
Among the installer checks is the quality of the pump plug contact on the printed circuit board.
Evidence: Saunier Duval GeniaSet FW 200-6 y FEW 200-6, instrucciones de funcionamiento, instalación y mantenimiento 0020291590_01
Virtual technician
Does F788 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
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