- Boilers
- Tankless gas water heater
F33
Vaillant F.33 on a gas water heater: air pressure switch error
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
On the Vaillant turboMAG plus water heater, F.33 is a manometric capsule error: the differential pressure switch that watches the flue draught. The fan, the wiring or the switch itself can cause it. If you smell fumes, switch it off and call a gas technician.
Safety first
Stop and check this first
- Gas smell with F.33 on the turboMAG plus: do not press switches or use a phone indoors, make no flame, open windows on your way, close the meter valve if you can reach it, get everyone out, knock on neighbours doors instead of ringing and phone the emergency services and the gas distributor from the street.
- An F.33 means the flue draught monitoring has failed: if a carbon monoxide (CO) alarm sounds or anyone feels a headache, dizziness, drowsiness or nausea, go outside at once, opening windows as you pass, and get urgent medical help from outdoors.
Safe checks you can perform
- If you smell fumes, ventilate and switch off
- Notice whether it matches strong wind
- Respect the 15 minute lockout
- Do not cover or alter the flue
Leave these tasks to a qualified professional
- Do not attempt this professional task: Test the differential pressure switch
- Do not attempt this professional task: Check the fan and wiring harness
- Do not attempt this professional task: Inspect the flue and measure CO
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.
Test the differential pressure switch
What they doThe gas technician checks whether the manometric capsule switches over when the fan starts and replaces the differential pressure switch only if it is defective.
They must show youhow they checked whether the switch responds.
In writingwhether the switch was replaced and why.
Check the fan and wiring harness
What they doThey check that the fan turns properly and test the harness continuity back to the board, then replace the fan or repair the wiring according to what they find.
They must show youthe result of the fan and harness test.
In writingthe part replaced or the cable section repaired.
Inspect the flue and measure CO
What they doBefore finishing, they check the air and flue duct for tightness, fixing and correct assembly and measure CO with test programme D.53; above 1500 ppm the gas flow pressure must be adjusted.
They must show youthe CO analyser reading.
In writingthe CO value and the flue condition.
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.
If you smell fumes, ventilate and switch off
- If F.33 comes with a smell of fumes in the home, follow section 1.3.4 of the user manual:
- open every door and window you can to create a draught, switch the heater off and call an authorised professional before using it again.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_00
Notice whether it matches strong wind
Note whether F.33 appears on very windy days or with gusts hitting the wall where the flue exits; the manual explains that very strong prevailing wind makes the appliance switch off. Do not touch the terminal: just describe the situation to the technician.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de instalación y mantenimiento 0020261986_00
Respect the 15 minute lockout
- If the heater detects the fault five times in a row within 15 minutes, it stays locked for another 15. Do not chain attempts:
- wait that long and try once to open and close the hot tap, switch off and on and press reset, as the manual describes.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_00
Do not cover or alter the flue
The user manual forbids any change to the exhaust installation and the air ducts. Simply check by eye that nobody has boxed in the heater or placed objects next to the flue outlet since it last worked properly.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_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
- Vaillant
- Product type
- Tankless gas water heater
Known code variants
- anomalía F33 Miele
- anomalie F33 Miele
- Bosch E33 espuma
- Bosch E33 foam
- Bosch F33 lavadora
- Bosch F33 washer
- Bosch washer F33 error
- code erreur F33 lave-vaisselle Miele
- E33
- error F33 lavadora Bosch
- error F33 lavavajillas Miele
- Error F33 Saunier Duval
- errore F33 lavastoviglie Miele
- F.33
- Fehlercode F33 Miele
- guasto F33 Miele
- Miele dishwasher F33
- Miele F33
- Miele fault F33
- Miele Geschirrspüler Fehler F33
- Saunier Duval F33
- St33
- Thema NOx F33
- turboMAG F.33
- turboMAG plus F33
- Vaillant F.33
- Vaillant F33 calentador
What it means
The turboMAG plus pushes its combustion gases out with a fan, and a differential pressure switch supervises that draught: the installation manual says it prevents excessive CO production and improves operation in windy weather. The error code table gives F.33 three possible causes: a defective fan, a break in the wiring harness and a defective differential pressure switch. The manual adds that very strong prevailing wind makes the product switch off, and that five faults in a row within 15 minutes lock it out for 15 minutes. The code alone does not tell which part has failed.
Warnings and stop conditions
- Criticaleditorial warning
Gas smell with F.33 on the turboMAG plus: do not press switches or use a phone indoors, make no flame, open windows on your way, close the meter valve if you can reach it, get everyone out, knock on neighbours doors instead of ringing and phone the emergency services and the gas distributor from the street.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_00
- Criticaleditorial warning
An F.33 means the flue draught monitoring has failed: if a carbon monoxide (CO) alarm sounds or anyone feels a headache, dizziness, drowsiness or nausea, go outside at once, opening windows as you pass, and get urgent medical help from outdoors.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_00
Symptoms and causes
Probable causes · in order
- Defective fanCommon
It is the first cause in the F.33 row: if the fan does not build the expected pressure difference, the switch does not change over, and the manufacturer remedy is a new fan.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de instalación y mantenimiento 0020261986_00
- Broken wiringPossible
A break in the wiring harness linking switch, fan and board is enough for the electronics to log the error; the technician should check the harness before swapping parts.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de instalación y mantenimiento 0020261986_00
- Faulty differential pressure switchPossible
The manometric capsule itself may be defective; for that case the table says to replace the differential pressure switch.
Evidence: Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de instalación y mantenimiento 0020261986_00
Virtual technician
Does F33 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
- 2
Vaillant turboMAG plus MAG ..5/1-5 RT, instrucciones de funcionamiento 0020261985_00
Vaillant · 2018 · manual
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