- Boilers
- Gas boiler
F83
Saunier Duval F.83 on a gas boiler: no sensor temperature rise
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Saunier Duval F.83 means that when the burner starts, the flow or return sensor shows little or no temperature change. Check the pressure: Saunier Duval recommends 1 to 1.5 bar. If it is low, top up; if it stays, call the service centre.
Safety first
Stop and check this first
- Top up with water suitable for heating and close the filling valve afterwards. Saunier Duval warns that very hard water or chemicals damage the appliance.
- If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, leave the building and call the gas company from a phone outside.
Safe checks you can perform
- Pressure on the display
- Top up with the filling valve
- Bleed radiators and reset
- Sensor and bleeding check by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Placement of the flow and return sensors
- Do not attempt this professional task: Real pressure and bleeding the appliance
- Do not attempt this professional task: Fault memory
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.
Placement of the flow and return sensors
What they doThe technician checks each sensor is on its own pipe, firmly fixed and in contact with it.
They must show youthe sensor in place and its reading when the burner starts.
In writingwhat was corrected and, if a sensor was replaced, why.
Real pressure and bleeding the appliance
What they doThe technician measures circuit pressure with a gauge and bleeds the appliance with test programmes P.07 and P.06.
They must show youthe measured pressure against the display.
In writingthe final pressure and whether a leak was found.
Fault memory
What they doThe technician reads the last 10 codes stored in the fault memory.
They must show youthe code list.
In writingthe codes found before clearing them.
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.
Pressure on the display
- Who:
- you.
- How:
- with no heating or hot water demand, look at the pressure indicator. Saunier Duval recommends 1 to 1.5 bar.
- Result that matters:
- whether it is low or flashes below 0.5 bar.
- If it is low:
- top up as in the next check.
- If it is correct:
- lack of water does not explain it all; go on to bleeding.
- Evidence to keep:
- a photo of the display with the pressure.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Top up with the filling valve
- Who:
- you.
- How:
- open the radiator valves, slowly open the filling valve under the boiler as the professional showed you, add water to 1 to 1.5 bar and close the valve.
- Result that matters:
- whether F.83 stops appearing and pressure holds.
- If it holds:
- it was lack of water; note the date.
- If it drops again:
- there is a leak; tell the official service centre.
- Evidence to keep:
- photos of the pressure before and after.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Bleed radiators and reset
- Who:
- you.
- How:
- if there is air, bleed the radiators as Saunier Duval describes and check the pressure again. Then press the reset key and wait five seconds.
- Result that matters:
- whether F.83 returns at the next start.
- If it does not return:
- it was water or air; watch the pressure for a few days.
- If it returns with correct pressure:
- call the official service centre.
- Evidence to keep:
- a photo of the display and the date.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Sensor and bleeding check by the technician
- Who:
- official service centre technician.
- How:
- checks real pressure, bleeds the appliance with the test programmes and checks the position and contact of the flow and return sensors on their pipes.
- Result that matters:
- whether water is missing or a sensor is badly placed.
- If a sensor was badly placed:
- it is refitted and a burner start is tested.
- If water was missing:
- the reason for the loss is traced.
- Evidence to keep:
- a report of what was checked.
The sensors are inside the boiler. Saunier Duval reserves inspection, maintenance and repair for a specialist installer: do not open the casing.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
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
- Boilers
- Brand
- Saunier Duval
- Product type
- Gas boiler
Known code variants
- caldera Vaillant F83
- Error F83 Saunier Duval
- error F83 Vaillant
- F.83
- Saunier Duval F.83
- ThemaFast Condens F.83
- Vaillant boiler F83
- Vaillant F.83
- Vaillant F83
What it means
In the ThemaFast Condens table, F.83 is fault: temperature change at the flow and/or return temperature sensors. When the burner starts, the boiler records no change, or only a minimal one, at the flow or return sensor. Saunier Duval gives two causes: little water in the appliance or a sensor wrongly placed on the pipe. If water is missing, heat does not reach the sensors properly. The code does not separate one cause from the other.
Warnings and stop conditions
- Mediumsource verified
Top up with water suitable for heating and close the filling valve afterwards. Saunier Duval warns that very hard water or chemicals damage the appliance.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Criticalsource verified
If you smell gas: Saunier Duval says to keep away from the area, open doors and windows, light no flames and do not smoke, do not touch switches, sockets, doorbells or phones, close the meter and appliance gas valves, leave the building and call the gas company from a phone outside.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Symptoms and causes
Probable causes · in order
- Little water in the applianceCommon
If the display shows low pressure and F.83 does not return after topping up, the cause was lack of water in the circuit.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00 · Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
- Flow or return sensor wrongly placedPossible
If there is enough water and F.83 stays, Saunier Duval points to a sensor wrongly placed on the pipe, so it does not sense the heat.
Evidence: Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Virtual technician
Does F83 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
Saunier Duval ThemaFast Condens, instrucciones de instalación y mantenimiento 0020238203_00
Saunier Duval · 2016 · manual
- 2
Saunier Duval ThemaFast Condens, instrucciones de funcionamiento 0020238204_00
Saunier Duval · 2016 · manual
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