- Boilers
- Gas boiler
F29
Saunier Duval F29 on a Thema NOx: ignition failure
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Saunier Duval F29 means ignition failure on the Thema NOx. Check the gas valve is open, switch the boiler out of service, wait 5 seconds and put it back into operation. If it persists, call the official service centre.
Safety first
Stop and check this first
- If you smell gas: do not use a flame to look for the leak, do not touch switches, a phone or anything that can spark, open doors and windows, close the gas valve, warn your neighbours and call your gas supplier's emergency number.
- Saunier Duval says not to repair or service the appliance yourself and not to run it until the official service centre has fixed the fault. Do not tamper with the safety devices.
Safe checks you can perform
- Gas valve and other gas appliances
- Out of service, 5 seconds, back on
- Ignition check by a gas technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Gas pressure and flame signal measurement
- Do not attempt this professional task: Combustion analysis and flue check
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.
Gas pressure and flame signal measurement
What they doThe technician measures inlet gas pressure with a manometer and checks the flame detection signal.
They must show youthe measured pressure against the rating plate and the flame reading.
In writingthe values and the cause found.
Combustion analysis and flue check
What they doAfter the repair, the technician runs a combustion analysis and checks the flue.
They must show youthe analyser printout.
In writingthe measured values and any part replaced with 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.
Gas valve and other gas appliances
- Who:
- you.
- How:
- check the boiler's gas valve is open and whether the gas hob lights. Do not touch anything inside the boiler.
- Result that matters:
- whether gas reaches the home and the boiler.
- If the valve was closed or there is no gas in the home:
- open it or call your distributor.
- If there is gas:
- the cause is in the boiler; go on to the restart.
- Evidence to keep:
- a photo of the valve and a note of whether the hob worked.
Evidence: Saunier Duval Thema NOx operating instructions
Out of service, 5 seconds, back on
- Who:
- you.
- How:
- switch the boiler out of service, wait 5 seconds and put it back into operation, as Saunier Duval says for F28 and F29.
- Result that matters:
- whether the burner lights and the indicator stops flashing red.
- If it lights and keeps running:
- note the date.
- If F29 persists:
- Saunier Duval says to contact the official service centre; do not repeat the cycle again and again.
- Evidence to keep:
- a photo of the code and a note of the time.
Evidence: Saunier Duval Thema NOx operating instructions
Ignition check by a gas technician
- Who:
- gas technician from the official service centre.
- How:
- measures inlet gas pressure, checks ignition, flame detection and the flue, and runs a combustion analysis.
- Result that matters:
- whether gas, ignition, detection and flue are within the manufacturer's specification.
- If gas pressure is low or flue gases do not clear:
- that confirms a cause outside the burner.
- If all of that is fine:
- it points to ignition or flame detection.
- Evidence to keep:
- a report with gas pressure, the combustion analysis and any part replaced.
Saunier Duval forbids the user from doing repairs or maintenance: gas, burner and electrodes are for the service centre only.
Evidence: Saunier Duval Thema NOx operating instructions
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
- 29
- code erreur F29 chaudière Vaillant
- codice F29 Vaillant
- código F29 Vaillant
- error F29 caldera Vaillant
- Error F29 Saunier Duval
- errore F29 caldaia Vaillant
- F 29
- Fehlercode F29 Vaillant
- Glow worm boiler F29
- Glow worm F29
- Glow-worm F.29
- Glow-worm F29
- Glow-worm F29 flame loss
- panne F29 Vaillant
- Saunier Duval F29
- Thema NOx F29
- Vaillant boiler F29
- Vaillant F.29
- Vaillant F29
- Vaillant Fehler F29
What it means
In the Thema NOx F25 operating instructions, Saunier Duval groups F28 and F29 as "ignition failure", with the fault indicator flashing red. The control has not established or kept a flame. Gas may be missing, there may be a flue or air problem, or ignition or flame detection may fail. The user remedy is to switch off, wait 5 seconds and switch on; the code does not say which of those systems failed.
Warnings and stop conditions
- Criticalsource verified
If you smell gas: do not use a flame to look for the leak, do not touch switches, a phone or anything that can spark, open doors and windows, close the gas valve, warn your neighbours and call your gas supplier's emergency number.
Evidence: Saunier Duval Thema NOx operating instructions
- Highsource verified
Saunier Duval says not to repair or service the appliance yourself and not to run it until the official service centre has fixed the fault. Do not tamper with the safety devices.
Evidence: Saunier Duval Thema NOx operating instructions
Symptoms and causes
Probable causes · in order
- Gas off or no supplyCommon
If the hob does not light either or the valve was closed, the cause is outside the boiler and the supply fixes it.
Evidence: Saunier Duval Thema NOx operating instructions
- Ignition or flame detectionPossible
If there is gas and the fault returns after each restart, ignition or detection remain suspects; the service centre checks it.
Evidence: Saunier Duval Thema NOx operating instructions
- Flue or air intakePossible
A blocked duct upsets the flame; Saunier Duval gives an air flow fault as F33, which is worth ruling out too.
Evidence: Saunier Duval Thema NOx operating instructions
Virtual technician
Does F29 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 Thema NOx operating instructions
Saunier Duval · 2012 · manual
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