Pressure dropping
F22: leak, valve or vessel.
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Saunier Duval Boiler: Servicing, Repair and Fault Codes
In short: In Belgium, Saunier Duval boilers are sold under the Bulex name: same appliances, same fault codes. Service Technic Belgium services and repairs both. Call 0477 03 88 98.
Is your Saunier Duval boiler showing a code, losing pressure or due for its service? Our engineers know this family of boilers well: it is very close to the Bulex units found in most Belgian homes. You know the cost before any work starts.
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Saunier Duval = BulexSame appliances
F22, F28, F29Explained
ServicingWith the attestation
PartsThrough the Bulex equivalent
Saunier Duval in Belgium: the Bulex brand
Saunier Duval is a French brand belonging to the Vaillant group. In Belgium the same group sells its boilers as Bulex: the models often carry the same names (Thema, Isotwin, Isofast, Semia) and share electronics, spare parts and the way faults are displayed.
We mostly meet boilers with a Saunier Duval badge in homes bought from French owners, in imported units, or where the installer worked on both sides of the border. Many expats moving to Brussels find one in their rented flat.
For our engineers it makes little difference: a Saunier Duval is repaired like a Bulex. See also our page on the Bulex heating engineer.
The models we service
ThemaPlus Condens and ThemaFast Condens are combination condensing boilers, the first with a small hot water store, the second heating water on demand. Isotwin Condens and Isofast Condens give more hot water for families with several bathrooms. Semia Condens is the simplest model.
Older fan-flue or open-flue boilers without condensing technology are still running in some houses, and we look after those too.
The exact reference is on the data plate, usually behind the front cover or under the boiler. Note it down before you call: it helps the engineer bring the right parts.
Fault codes F22, F28 and F29
On recent Saunier Duval boilers a fault shows as an F followed by a number. F22 means a lack of water: the pressure is too low, often because of a small leak, a dripping safety valve or an expansion vessel that has lost its charge.
F28 means the boiler failed to light: gas supply, electrode, ignition lead or circuit board. F29 means the flame went out while running, often linked to the flue or a blocked condensate trap.
You can top the system up to about 1.5 bar when cold and reset once. If the code comes back, do not keep resetting: call us. The full list is on our French page about Saunier Duval fault codes.
Servicing a Saunier Duval boiler
During the service the engineer cleans the burner and the heat exchanger, flushes the condensate trap, checks the electrode, the expansion vessel and the flue, then measures the combustion with an analyser.
You receive the maintenance attestation; how often the service is required depends on your region. Brussels asks for a periodic check of gas boilers every three years and of oil boilers every year, but a yearly service keeps a condensing boiler in better shape.
If you rent, keep the attestation: your landlord or the managing agent will ask for it, and so may your insurer after a claim.
Repair or replace
Some Saunier Duval parts are slower to obtain in Belgium than in France. We tell you at the diagnosis and look first for the equivalent Bulex part at our suppliers.
When a very old boiler is no longer worth repairing, we suggest a modern condensing boiler or a heat pump, with a free and detailed quote.
If you are unsure, the engineer compares for you: what the repair costs, how old the boiler is and what a new installation would change. The decision is yours.
The problems we hear about most
Pressure dropping (F22): a small leak, the safety valve or the expansion vessel. No ignition (F28): gas, electrode or circuit board. Flame going out (F29): flue or condensate trap.
Lukewarm hot water: a scaled domestic hot water exchanger or a sticking diverter valve. A noisy boiler: limescale in the exchanger or a tired circulating pump.
If you recognise one of these, say so on the phone: the engineer will arrive better prepared.
What we see most often
No ignition
F28: gas, electrode or board.
Flame going out
F29: flue or condensate trap.
Lukewarm water
Scale or diverter valve.
Before you call
The data plate
Model and year of the boiler.
The code
A photo of the display.
The pressure
The figure on the gauge.
The last service
When and by whom.
How a visit works
You call or book
Describe the problem; a photo of the unit or of the code on the display, sent on WhatsApp, helps the technician prepare.
Call-out cost first
The office tells you what the visit costs and when the technician will come, before anyone sets off.
Your agreement first
On site, the technician explains what he found and what the repair costs, then waits for your yes. Job sheet and invoice at the end.
What our customers say
Saunier Duval and Bulex across Belgium
We service and repair Saunier Duval and Bulex boilers in Brussels, Wallonia and Flanders.
BrusselsWalloon BrabantFlemish BrabantHainautNamurLiègeLuxembourgAntwerpEast FlandersWest FlandersLimburg
Frequently asked questions
Are Saunier Duval and Bulex the same?
Both brands belong to the Vaillant group and share many models and parts. In Belgium, Bulex is the name you see most.
What does F22 mean on my Saunier Duval?
Low water pressure. Top up to about 1.5 bar when the system is cold; if the code returns, there is a leak or the expansion vessel needs attention.
And F28?
The boiler failed to light. Check that the gas is on; if the fault returns, the electrode, ignition lead or circuit board need checking.
Are you the Saunier Duval after-sales service?
No, we are Service Technic Belgium: we repair and service Saunier Duval and Bulex boilers like every other brand.
Can you find the parts in Belgium?
Yes, usually through the Bulex equivalent at our suppliers. If a part takes longer, we tell you at the diagnosis.
How long does a service take?
About an hour for a boiler serviced every year, longer if it has not been opened for some time.
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.
Your Saunier Duval will not start?
Call 0477 03 88 98 with the code on the display: an engineer comes to find the cause. For a replacement, ask for a free quote.