F.28
Ignition failed.
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Saunier Duval Fault Codes: F.22, F.28 and the Other Codes Explained
In short: Saunier Duval belongs to the same group as Vaillant and Bulex: in Belgium many of its boilers are sold as Bulex, with the same codes. A heating engineer comes with the cost given first. Call 0477 03 88 98.
Is your Saunier Duval (Thema Condens, ThemaPlus Condens, ThemaFast Condens, Isofast…) showing a code starting with F, such as F.22 or F.28? Below you will find what each code means and what the engineer checks.
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F codesExplained
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A Saunier Duval boiler showing a fault
Saunier Duval wall-hung boilers are common in Belgian houses and flats, often fitted ten or fifteen years ago. The Thema Condens and ThemaPlus Condens are the most frequent. Their codes all start with the letter F, followed by a dot and two digits.
F.28 (ignition failure) and F.22 (lack of water) are by far the most common. F.29 points to a flame going out while running, F.75 to a pump that creates no pressure change at start-up. Codes F.00 to F.11 concern the temperature sensors.
Our heating engineer checks the ignition, the ionisation, the gas valve, the pump, the pressure sensor and the sensors. He tells you what he found and the repair cost before doing it.
Codes F.00 to F.24
F.00 / F.01 — Flow or return sensor open circuit. The sensor concerned, its connector and wiring.
F.10 / F.11 — Flow or return sensor short circuit. The sensor concerned and its wiring.
F.20 — Overheat thermostat triggered. Water circulation, pump, flow sensor.
F.22 — Not enough water in the system. Pressure, possible leak, pressure sensor, pump.
F.23 — Temperature difference too large (pump, air in the appliance). Pump, air in the circuit, water flow.
F.24 — Temperature rising too fast. Pump, flow, system valves.
These codes apply to the Thema Condens and boilers of the same generation; older non-condensing Saunier Duval boilers may differ.
Codes F.27 to F.75
F.27 — Flame simulation: flame detected when there should be none. Electrode, gas valve, circuit board.
F.28 — Ignition failed at start-up. Gas supply, ignition and ionisation electrode, gas valve, condensate trap.
F.29 — Flame lost while running and relighting failed. Gas pressure, ionisation, flue.
F.32 — Fan fault. Fan, wiring, circuit board.
F.35 — Flue fault (blocked balanced flue). Balanced flue, flue duct, outdoor terminal.
F.61 / F.62 — Gas valve control fault / delayed shut-off. Gas valve, circuit board.
F.63 — Memory fault (EEPROM). Circuit board.
F.73 — Water pressure sensor signal too low. Pressure sensor and wiring.
F.75 — No pressure change detected when the pump starts. Pump, air in the system, pressure sensor.
Code not in this list? Call us: the engineer knows it.
Servicing a Saunier Duval boiler
A Thema Condens that shows F.28 again and again often has a blocked condensate trap, a worn electrode or a dirty burner. Regular servicing prevents most of these stops.
The engineer cleans the burner and the exchanger, checks the trap, the expansion vessel and the balanced flue, measures the combustion and leaves you the service attestation.
He also tells you the condition of the pump and the diverter valve, two parts that wear on Saunier Duval boilers more than ten years old.
Typical faults
Ignition (F.28, F.29): a worn electrode, a blocked trap, low gas pressure or a tired gas valve. Lack of water (F.22, F.75): a leak, the expansion vessel, the pump or the pressure sensor.
Overheating (F.20, F.23, F.24): a weak pump, air or sludge in the circuit. Sensors (F.00 to F.11): a sensor open or short-circuited, often after years of use.
Flue (F.35): a balanced flue blocked by a nest, leaves or ice. Note the code with its two digits: the engineer can then bring the matching parts.
What the engineer does
He reads the code and the memory: the service menu keeps the last faults, so he sees what keeps coming back. Then he measures ionisation, gas pressure, pump and sensors, to find the cause before changing a part.
You get the cost before the repair, then the repair itself, a combustion analysis, the job sheet and the invoice.
Smell gas? Do not touch any switch, open the windows, leave the home and call 112 from outside.
The codes we see most
F.22
Lack of water.
F.29
Flame lost.
F.75
No pressure change at the pump.
When you call
The code
With its two digits.
The model
On the data plate.
The pressure
The figure on the gauge.
Last service
Date on the attestation.
From your call to the invoice
A short call
Address, appliance, what is wrong: the office writes it down and books a time.
No surprises
You know the call-out cost before anyone leaves; a replacement or a new installation gets a written quote.
On site
Diagnosis and explanation first, then your agreement, then the work. The documents come from Service Technic Belgium.
What our customers say
Where we work
We repair Saunier Duval and Bulex boilers across Belgium, in Brussels, Wallonia and Flanders.
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Frequently asked questions
What does F.28 mean on a Saunier Duval?
The boiler failed to light its burner. Gas, electrode, gas valve or condensate trap need checking: note the code and call us.
What does F.22 mean?
There is not enough water in the system. If the code returns, a leak or an expansion vessel problem must be found.
What is the difference between F.28 and F.29?
F.28: ignition failed at start-up. F.29: the flame went out while running and did not relight.
Do Saunier Duval and Bulex have the same codes?
Yes for many models: Bulex is the name under which Saunier Duval is sold in Belgium.
The code comes back after a restart: what should I do?
Note the code and call us. Restarting the boiler several times does not fix the cause.
When can you come?
We offer the first available slot, depending on your municipality, with the cost given first.
How do I book?
Call 0477 03 88 98, send us a WhatsApp message or book online with the « Book an appointment » button. Tell us the municipality and, in a few words, what is going on.
Is your Saunier Duval showing a code?
Call 0477 03 88 98 or book online: a heating engineer comes with the common Thema Condens parts.