Boiler · Naples and Campania
Boiler not making hot water: causes and what to do
You open the tap and the water stays cold, or it turns hot and then cold halfway through the shower. On wall-mounted boilers the typical causes are few: too little water coming in, a sensor that does not notice the draw, a heat exchanger full of limescale. With a video call we rule out the simple causes and work out whether a part is needed.
From €110 + VAT about 1 hourCleaning, flue gas check and logbook. Compliance sticker (bollino) is extra
The flow switch and the heat exchanger are inside the boiler, next to the gas and electrical parts: do not open it to clean them. If you smell gas while checking, stop: no lights, switches or flames, windows open, gas closed at the meter if you can do so safely, then leave the house and call your distributor's free number from your bill (Italgas 800 900 999, free, 24 hours a day) or 112.
Recognise the problem
- You open the hot tap and the boiler does not light, the flame symbol does not appear
- The water turns hot and then cold during the shower
- It only runs hot if you open the tap fully
- The radiators heat but cold water comes out of the tap
- The hot water arrives in waves, hot and then lukewarm
The most common causes
- 1
Flow switch dirty or faulty
The flow switch is the sensor that notices you have opened a tap and starts the boiler. If limescale or dirt slows it down, the boiler does not start or only starts with a strong flow.
- 2
Domestic hot water heat exchanger scaled up
This is the plate where the tap water picks up heat. With hard water it fills with limescale: the water heats poorly and the boiler goes into protection.
- 3
Three-way valve stuck
This is the valve that sends hot water either to the radiators or to the taps. If it stays on heating, the radiators warm up and the tap stays cold.
- 4
Too little water coming in
A half-closed stop valve, a clogged filter or an aerator full of limescale reduce the flow below the level that starts the boiler.
- 5
Hot water probe
A temperature probe that reads wrongly makes the burner switch off too soon or stay on longer than it should.
What you can safely check yourself
- Try several taps: if hot water is missing at only one, the problem is in that tap and not in the boiler.
- Watch the display while you open the hot water and note whether the flame appears, a code appears or nothing happens.
- Check the temperature set for hot water and that the function has not been switched off from the boiler buttons.
- Read the pressure: with the system empty, many boilers will not even start for the taps.
- If a code appears, press reset once and try again.
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
- The boiler does not react when you open the tap, even with the right pressure
- The hot water comes and goes even with the tap fully open
- The radiators heat but the taps do not, or the other way round
- Besides the poorly heated water you hear whistling or gurgling from the boiler
How much it costs
Boiler service and flue gas analysis (our price)
Cleaning, flue gas check and logbook. Compliance sticker (bollino) is extra
from €110 + VAT
Hot water repair (flow switch, heat exchanger, valve)
indicative market price in the Naples area; a heat exchanger costs more than a flow switch
40-250 €
Market figures are indicative for the Naples area. You know our exact price before we start; prices apply near our base in Parete, and further away you see them in full when you choose your town.
It cuts out during the shower: why it happens
A boiler that goes off halfway through a shower has usually stopped sensing the flow, or has overheated. In the first case, when you turn the mixer a bit towards cold the flow falls and the flow switch, if dirty, drops out.
In the second case there is almost always limescale. A scaled-up heat exchanger cannot give up its heat, the internal temperature rises and the boiler switches off the burner to protect itself. After a few seconds it restarts, and the water arrives in waves.
A clue to tell the two apart: if the water turns hot again when you open the tap further, we suspect the flow. If it gets worse exactly with very hot water, we suspect the heat exchanger.
Limescale and hard water in Naples
Water hardness is measured in French degrees (°F). In Naples it varies a lot from area to area, and in the Vesuvius area it is often above 35-40 °F. Above 35 °F limescale speeds up heat exchanger failures, because it settles exactly where the water is heated.
A scaled-up heat exchanger can be flushed or replaced. If the problem comes back, it is worth considering a limescale treatment on the cold water entering the boiler. You can find the hardness in your area in the analyses published by the water supplier.
Want to know what it is first? Show us
On video we check the hot water settings, the pressure and what happens on the display when you open the tap, and this is enough to rule out many causes. The flow switch, the heat exchanger and the three-way valve, however, are checked at your home, with the boiler opened by us.
Video consultation, up to 15 minutes: €9.90 (€14.90 on Sundays), deducted from the bill if we then come to your home.
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Frequently asked questions
Why does the boiler not start when I open the hot water?
Usually because not enough flow arrives or because the flow switch does not detect it. It can also be due to low pressure or a lockout. If the display does not react at all when you open the tap, the sensor is the first suspect.
The radiators work but the hot water does not: what has broken?
Often the three-way valve, which decides where to send the hot water, or the flow switch. These are internal parts: on a video call we narrow it down, then the check is done at your home.
Intermittent hot water: is it limescale?
It is the most common cause on boilers a few years old, especially where the water is hard. A tap with a limescaled aerator can give the same effect, and it is the first thing to rule out.
Can the heat exchanger be cleaned instead of replaced?
Sometimes yes, with a chemical flush or by removing it. If it is heavily scaled or perforated, replacing it is better. We assess it after seeing it and tell you the price before we start.
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