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Boiler Lockout: Causes and Solutions
Your boiler locks out, a red light comes on and it asks to be reset, sometimes several times a day? A lockout is not the fault itself: it is the boiler protecting you. Our engineers find what triggers it and repair it, 7 days a week.
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Safety explainedFlame, overheat, flue
All brandsGas and oil
Price given firstBefore any repair
7 days a weekEvenings and weekends
Flame failure: the boiler cannot see the flame
The most common lockout is flame failure. At each start the boiler opens the gas, makes a spark and must detect a flame within a few seconds. If it does not, it shuts the gas and locks out: code F28 or F29 on Vaillant, 6A on Buderus, E133 on Remeha.
The causes are well known: insufficient gas supply, worn ignition electrode, dirty flame sensor, poor earth or a faulty gas valve. A boiler that locks out mainly in the morning or in hard frost may also have a frozen condensate pipe.
The engineer measures the gas pressure during ignition and the flame current. Those two figures often point to the faulty part. He cleans or replaces it and restarts the boiler several times to check it lights every time.
Flue safety: poor extraction
Boilers also monitor the removal of combustion gases. A pressure switch or flue thermostat shuts the appliance down if the gases are not leaving properly. It is an essential protection against carbon monoxide.
A flue blocked by a nest, debris or soot, an iced-up wall terminal, a dirty fan or a split pressure switch tube trigger this safety. Sometimes it only happens in strong winds, when air pushes back down the flue.
The engineer checks the fan, the pressure switch and the draught, then carries out a combustion analysis in the flue. If the flue itself needs cleaning or modifying, he tells you clearly. Never bypass this safety device: it is there for your health.
Oil burner lockout
On an oil boiler, a lockout shows as the red light on the burner. The burner tried to start, the photocell saw no flame and it stopped. It happens after running out of oil, with a blocked filter, a clogged nozzle or a sooty photocell.
You may press the reset button once. If the burner locks out again, do not keep trying: atomised oil that did not burn builds up and makes the next ignition dangerous.
The technician cleans the photocell, checks the oil pump and suction line, replaces the nozzle and filter if needed and adjusts the burner. If the lockout came from an empty tank, he advises having the filter checked after the delivery.
Other safety devices that lock a boiler out
Not all boilers have the same protections, but these are found on almost all of them.
Low water
Below about 0.8 bar the boiler stops so as not to run dry. Bring the pressure to 1.5 bar when cold.
Condensate
The condensate trap is full or frozen: the boiler shuts down before water reaches the combustion chamber.
Faulty sensor
A temperature sensor giving a wrong reading makes the boiler think it is overheating.
Electrical supply
Live and neutral swapped, or a missing earth, stop some boilers detecting the flame.
Our visit
Code and frequency
Give us the code shown and tell us when the boiler locks out.
Finding the cause
The engineer measures gas, flame, flue and circulation, then gives the repair price.
Operation checked
He repairs, runs several cycles, checks the combustion and hands you the job sheet.
What our customers say
Where do we work?
Our heating engineers work all over Belgium: Brussels, Flanders and Wallonia. For a boiler in lockout, call us to find out the first available visit.
BrusselsWalloon BrabantFlemish BrabantHainautNamur provinceLiège provinceLuxembourg provinceAntwerpEast FlandersWest FlandersLimburg
The brands we work with
Our technicians work on all brands: they install, service and repair appliances from the major manufacturers. For a new installation, we recommend the model that suits your home and budget.
We buy our equipment from all the major Belgian wholesalers and suppliers, including Facq, Van Marcke and Desco: genuine parts, quickly available.
Frequently asked questions
Is it serious if my boiler locks out?
The safety device is doing its job. What matters is the reason: one isolated reset is not worrying, repeated lockouts mean a part needs repairing.
How many times can I reset?
Once. If it locks out again, stop and call us on 0477 03 88 98. Repeated resets can make the fault worse, especially on oil.
My boiler only locks out in the morning. Why?
Often a condensate pipe that freezes overnight, or harder ignition when everything is cold. The engineer checks the drain and the ignition.
Can I bypass a safety device to get heat?
No, never. A disabled safety device can cause overheating, an explosion or carbon monoxide poisoning.
Does servicing prevent lockouts?
It prevents many: clean electrodes and burner, cleared trap and correct combustion. It is the best prevention.
Do you repair all brands?
Yes: Vaillant, Bulex, Viessmann, Buderus, Remeha, Junkers, Saunier Duval, ACV, Atag, Intergas and others, gas and oil.
What does a lockout cost to fix?
It depends on the cause: cleaning a sensor is quick, a gas valve or a board costs more. The engineer gives you the price after the diagnosis and before starting the repair.
Boiler still locking out?
Call us for a repair, book a slot online or request a quote.