Central heating boiler losing pressure or no hot water: what now?
Do you have to keep topping up the central heating, or is there no more hot water? Often it's a matter of water pressure or bleeding — sometimes a leak or breakdown.
A healthy central heating system stands at approximately 1.5 bar when cold. If the pressure drops, the boiler heats poorly or shuts down. If the pressure keeps dropping, water is leaking somewhere in the system.
Boiler pressure, bleeding and breakdown
A few checks will quickly point you in the right direction.
Read the water pressure
On the pressure gauge or display. Below ~1 bar → top up to approximately 1.5 bar using the filling valve.
Does the pressure keep dropping?
Then the system is leaking — at a radiator, coupling or the boiler. Leak detection or repair is needed here.
Bleed the radiators
Cold spots at the top of the radiator? Bleed it, then check the pressure again.
Heating works, no hot water
Often indicates the hot water heat exchanger or a setting. Have it checked.
Error code on the display
Note the code — it tells the technician immediately the direction of the fault.
Annual maintenance
Regular maintenance prevents breakdowns, keeps the boiler efficient and is safer against carbon monoxide.
Where is the water going? Causes of pressure loss and what the technician does
A central heating system is a closed system. The water circulates between boiler and radiators and should not escape. If the pressure keeps dropping anyway, water is disappearing somewhere. Sometimes you see that immediately, but often it happens in a place you don't look.
Common causes
- Just bled. After bleeding radiators, the pressure always drops a little. Topping up once is then normal.
- A leaking valve or coupling. Check radiator valves and couplings for limescale rings, rust marks or a damp floor.
- The expansion vessel. When water heats up, it expands. The expansion vessel absorbs this. If the vessel no longer works properly, the pressure rises sharply when heating and drops again when the boiler cools down.
- The pressure relief valve. If the pressure is too high, this valve releases water to the drain. You sometimes see this from a dripping discharge pipe or funnel under the boiler. The water then disappears unnoticed into the sewer.
- A leak in a pipe in the floor or wall, for example with underfloor heating or pipes in the crawl space.
How to help the technician
Write down for a few days what the pressure is when the boiler is cold and when it's warm. Also note how often you need to top up. Top up according to your boiler's manual and fill the filling hose with water first, so that no air enters the system. Turn the filling tap off properly afterwards and disconnect the hose. Never open the casing of the boiler: behind it are gas components and that is work for a tradesman.
When the technician needs to come
- You have to top up regularly, for example every few weeks.
- The pressure rises sharply when heating and then drops again.
- There is water under or next to the boiler.
- The boiler keeps showing the same fault code or locks out.
The technician first checks the expansion vessel and restores it to the correct pre-charge pressure if necessary. Then he checks the pressure relief valve, the couplings and the valves. If he finds nothing there, a leak in the pipes or underfloor heating is likely. We then locate the exact spot with measurements, without unnecessary breaking. You can read more about breakdowns and repairs on our central heating boiler page.
Related services
Need help? View the related service or call us directly.
What the technician does for pressure loss, and what it costs
Pressure loss means that water is escaping from the system somewhere, or that the expansion vessel is no longer doing its job. The technician investigates this step by step. First we check the pressure relief valve: if it's dripping, the pressure during heating is too high. Then we measure the pre-charge pressure of the expansion vessel and look at the boiler, the manifold and the radiators for signs of leakage, such as limescale marks or rust.
If nothing is visible anywhere, the leak may be in a floor or wall. We then use leak detection to find the leak without unnecessary breaking. It often turns out to be a small leak at a radiator valve or a coupling.
If you keep topping up without finding the cause, fresh water with oxygen and limescale keeps entering the system. This accelerates wear on the boiler. So have it checked in good time.
Good to know
Short answers to questions we're often asked.
Topping up once after bleeding is normal. If you have to top up regularly, for example every few weeks, water is escaping from the system. Then have it checked where it's going.
Hot water expands. A slight rise is normal, because the expansion vessel absorbs that. If the pressure rises sharply, the expansion vessel often no longer works properly. Have this checked by a technician.
The water can go unnoticed to the drain via the pressure relief valve. It can also leak from a pipe in the floor, the wall or the crawl space. Leak detection then helps to find the spot without breaking.
Check whether the hot water function of the boiler is on and whether the tap is open far enough. If it still does not work afterwards, the fault is often in the hot water section of the boiler. That is work for a technician.
No. Behind the casing are gas and electrical components. You can top up and bleed yourself. Everything inside the boiler should be left to a tradesman.
For a boiler breakdown we quote a guide price of €90 to €175. If the leak needs to be found with leak detection, €120 to €225 applies. You'll be told in advance what it costs.
The water can drain away unnoticed via the pressure relief valve, or through a small leak in a floor or wall. A faulty expansion vessel also causes pressure fluctuations. The technician measures this step by step.
Need help in The Hague or the Randstad?
Feel free to call us for advice or an appointment. In emergencies we're available 24/7.
Need help straight away? Our technicians in The Hague and surrounding area can help you via central heating boiler — call 070 783 0224.