Water heater · Naples and Campania
Gas water heater won't light: what to do
You open the hot tap, hear the ignition clicks, and then nothing. The flame does not light, or it lights and goes out after a few seconds. The cause is often simple, such as flat batteries or too little water flowing. You should not test the gas parts yourself, so we help you see how far you can safely go.
From €170 + VAT about 2 hoursReplacement: labour from €120, appliance not included
Do not open the casing of a gas water heater and do not touch the valve, burner or flue. If it switches off during use, ventilate the room and wait about ten minutes before relighting it. If it happens again, do not use it until it has been checked. If you smell gas, do not switch on any lights or appliances. Go outside and call the gas distributor's emergency line from there.
Recognise the problem
- You hear the ignition tick but there is no flame
- The flame lights and goes out after a few seconds
- It only lights if you open the hot tap fully
- The display of the Vaillant turboMAG plus shows F.28 or F.33
- It switches off halfway through a shower and restarts after a while
- No sign of life: no clicks and no lights
The most common causes
- 1
Flat batteries
Many open-chamber gas water heaters light the flame using two large batteries. When they run down, ignition gets slower and then stops altogether. In the Bosch Therm 4000 manual, for example, this is the first entry in the troubleshooting table.
- 2
Too little water flowing
An instant water heater only starts above a minimum water flow. On the turboMAG plus, for example, it is 2.5 litres per minute. A tap aerator clogged with limescale, a dirty inlet filter or low pressure in the home may not be enough.
- 3
Gas not arriving
A closed tap, an empty cylinder or gas pressure that is too low all give the same symptom: clicks with no flame. If the kitchen hob also struggles, the problem is upstream of the water heater.
- 4
Flue safety tripped
Open-chamber units have a device that puts the flame out if the fumes are not leaving the flue properly. When it trips, the fault is in the flue and the draught, not in the ignition.
- 5
Fan or pressure switch
In models with a fan, such as the turboMAG, the fumes are pushed out and a pressure switch, an air-pressure sensor, checks that this is happening. If either one fails, the water heater locks out and shows a code.
What you can safely check yourself
- Change the batteries for new ones of the same type, if the compartment opens from outside without tools
- Check that the gas tap near the water heater is open and that the hob lights
- Unscrew the aerator on the hot tap and see whether it is clogged with limescale
- Try opening the hot tap further and see whether the ignition changes
- Note the code on the display and when it appears
Never open the boiler or the gas water heater, and always switch off the power before touching an electrical appliance. If in doubt, call us.
When you need a technician at home
- With new batteries the flame still does not light
- The water heater switches itself off during use, more than once
- The display reports a pressure switch or fan fault
- You see a yellow flame, soot or dark marks above the unit
- The flue or chimney needs checking
Vaillant turboMAG plus: what F.28, F.29 and F.33 mean
The installation and maintenance manual for the turboMAG plus lists F.28 as a failed ignition at start-up. The causes it gives are no gas arriving, gas pressure that is too low, too little combustion air or a faulty earth connection. F.29 is the same ignition failure, but when the unit was already running.
F.33 is a pressure switch error. The manual links it to a faulty fan, a broken cable or a pressure switch that needs replacing. All of these are jobs for a technician. Pressing the reset button repeatedly does not help, and if the resets pile up, the unit stops with another code.
One useful detail: this model cuts the gas by itself if it stays on continuously for more than 45 minutes, so after a very long shower the shutdown may be intentional. The atmoMAG units, on the other hand, are open-chamber: there the chimney draught and the ignition matter most.
Why we stop at external checks on the gas parts
A gas water heater that does not light is not dangerous in itself. It simply does not heat. The risk comes when someone tries to get it going at all costs by taking off the casing or forcing the safety devices.
The device that monitors the fumes is there to stop carbon monoxide, a gas with no smell that you cannot see, from staying in the room. If the water heater switches off during use, manuals such as the Bosch Therm 4000 say to ventilate the room, wait about ten minutes and switch it on again. If it happens again, the flue must be checked before you use it once more.
Want to know what it is first? Show us
On video we watch what the water heater does when you open the tap: whether it clicks, whether the flame shows in the sight glass, whether the display shows a code. We guide you in changing the batteries and checking the water flow, without opening the unit. If the problem is in the gas valve, the fan or the flue, we book the visit and the €9.90 is deducted from the bill.
Video consultation, up to 15 minutes: €9.90 (€14.90 on Sundays), deducted from the bill if we then come to your home.
Book the consultationDIY guides
Frequently asked questions
How often should I change the batteries in a gas water heater?
There is no fixed interval, it depends on how much you use it. The typical sign is ignition that gets slower and clicks more than usual. It helps to keep two spare batteries at home in the size shown in the manual or on the compartment.
Why does it only light with the water fully open?
Because little water is flowing and the water heater stays under the minimum flow it needs to start. Often it is enough to clean the tap aerator or the inlet filter. If the water is weak at every tap in the home, the problem may be mains pressure.
Can I reset the turboMAG myself?
Yes, the turboMAG plus has a reset button to restart after a fault. If the code returns straight away, pressing again is pointless. The fault has to be found, and the button does not repair it.
Is it dangerous if the water heater won't light?
Usually not, it simply does not heat. Stop using it if it switches off on its own during use, if you see soot or a yellow flame, or if you smell gas. In that case your safety and the distributor's emergency line come before any video call.
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