Boiler · Naples and Campania
Boiler with low pressure: what to do
The boiler works with the water in your radiators under pressure. With the system cold, the typical value is between 1 and 1.5 bar, but the right one for your boiler is written in the manual. If it drops too far the boiler locks out. You can top it up yourself, and if the pressure falls again we look for the reason together.
From €110 + VAT about 1 hourCleaning, flue gas check and logbook. Compliance sticker (bollino) is extra
Under the boiler there are both the water pipes and the gas pipe, often with taps that look alike. Touch only the filling valve shown in the manual and, if in doubt, stop and ask. Do not open the casing to look for the expansion vessel: inside there is gas and electricity.
Recognise the problem
- The gauge needle is below 1 bar or the display shows a low value
- The boiler locks out with the low-pressure code
- You top up the pressure and a few days later it is down again
- Water comes out of the drain pipe under the boiler
- The pressure rises a lot when the boiler heats and collapses when it cools
The most common causes
- 1
Bleeding the radiators
When you bleed the radiators, air comes out, but a little water too. The pressure drops and needs topping up. This is normal if it happens once and no more.
- 2
Small leak in the system
A drip from a fitting, a radiator valve or a pipe under the floor is enough to bring the pressure down within a few days.
- 3
Expansion vessel discharged
The expansion vessel is a tank with a membrane and an air cushion that absorbs the expansion of the water as it heats. If the cushion empties, the pressure rises too much when hot, the safety valve discharges, and when cold the needle collapses.
- 4
Leaking safety valve
This is the valve that opens at around 3 bar to protect the system. If it opens often or gets dirty with limescale, it keeps letting water out when it should not.
What you can safely check yourself
- Read the pressure with the system cold, with the boiler off for a while, and note the value.
- Look in the manual for the recommended value for your model.
- Slowly open the filling valve under the boiler and close it tightly as soon as the needle reaches the manual value, without going over it.
- If the boiler was locked out, press reset once after topping up.
- Write down the date: if the pressure is low again after a few days, there is a cause to find.
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
- You have to top up more than once a month
- Water comes out of the safety valve or the drain pipe under the boiler
- When hot, the needle gets close to 3 bar
- The pressure rises by itself even with the boiler off, a sign that the filling valve does not close properly
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
Pressure-related repair (vessel, valve, leaks)
indicative market price in the Naples area; you top up yourself, you only pay if a part needs fixing
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.
How to top up the boiler pressure
The filling valve is almost always under the boiler, among the pipes. It can be a knob, a lever or a butterfly screw. On some recent models the top-up is controlled from the display. The manual shows it with a drawing.
Do it with the boiler cold. Open the valve a little at a time and watch the needle, which rises in a few seconds. Close it tightly when you reach the indicated value. If you overshoot, the extra water will be discharged by the safety valve when the boiler heats up.
If you are not sure which valve is the right one, do not turn valves at random. On a video call we point it out to you, looking at the pipes on your model.
Why the boiler pressure drops
A healthy system holds its pressure for months. If it drops every week, water is leaving somewhere. Sometimes the leak is visible, like a stain under a radiator. Other times it is not, because it drips inside the boiler or ends up in the drain through the safety valve.
A useful clue is how the needle behaves. If it rises a lot when hot and collapses when cold, the expansion vessel has almost certainly lost its charge. If it drops slowly even with the boiler off, a leak in the pipes or radiators is more likely.
In both cases topping up is only a remedy for today. The expansion vessel is recharged or replaced by opening the boiler, so it is a technician's job.
Want to know what it is first? Show us
We show you where the filling valve is on your model and stay on the line while you top up, so you stop at the right point. Then we talk about how often it happens: if the pressure falls again, we tell you whether the most likely cause is a leak or the expansion vessel.
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
What is the right boiler pressure?
With the system cold, usually between 1 and 1.5 bar, but what counts is the value written in the manual for your model. In multi-storey houses a slightly higher value may be needed, and the technician who knows the system sets it.
How often is it normal to top up?
Once or twice a year, for example after bleeding the radiators, is normal. If you have to do it every week or every month, there is a leak or the expansion vessel needs checking.
It leaks water from the relief valve: what does that mean?
That valve, also called the safety valve, opens when the pressure goes over the limit. If it drips, usually the pressure rises too much when hot because of the expansion vessel, or the valve is dirty and no longer closes properly. In both cases you need a visit.
I put in too much pressure, what do I do?
If you are just above the recommended value, usually nothing happens. If the needle gets close to 3 bar, call us and we guide you on a video call to bring it back to the right value.
You may also be interested in
Boiler all over Campania
We work in Naples, Posillipo, Caserta and all over the region. Near our base in Parete there is no travel cost; further away you see the full price before you confirm.
Ready when you need us.
Book your visit by choosing a day and time. For emergencies we answer 24 hours a day, across Campania.