Topping up means allowing more water into the central heating system to repressurise it. The boiler needs the correct pressure to work properly. You may need to do this if you have had a leak in the boiler, pipework or radiators. If the system is working properly, you should only have to increase the boiler pressure once or twice a year.
Can You Top Up A Boiler When It Is On?
Key Takeaways
- Topping up a boiler: Adding more water to the central heating system, often necessary after a leak in the boiler, pipework, or radiators.
- Topping up when the boiler is on: Not recommended as it can result in inaccurate system pressure readings and incorrect water levels. It’s important to turn off the boiler and let it cool down before topping up.
- Water pressure maintenance: Modern combination boilers maintain water pressure through the filling loop connected to the cold water mains.
- Ideal boiler pressure: When heating is on, pressure ranges from 1 to 2.5 bar. When the boiler is off, the pressure is typically between 0.75 and 1.5 bar.
- Regular topping up indicates an issue: Regularly topping up suggests a water leak or reduced pressure after bleeding a radiator. Professional help may be needed to fix the problem.
Can you top up a boiler when it is on?
It is not recommended to top up a boiler with water when it is powered on. If boiler pressure drops too low, below 1.0 bar, it needs to be repressurised. Before adding water, the boiler should be turned off and pipework cooled to avoid safety hazards. With the unit off, topping it up with water to increase pressure only takes a quick moment.
To top up a boiler with fresh water and increase pressure, you should not top it up when it is on. This is because it won’t give you an accurate system pressure reading and you could end up not putting enough water in, or too much. It’s important to turn off the boiler and let the heating system cool down before you top-up.
In most modern combination boilers, the water pressure is maintained by the filling loop which can be either externally or internally connected to the cold water mains.
What pressure should my boiler be?
When the heating is on, the pressure can be anywhere between 1 and 2.5 bar. Your boiler user manual will tell you what the ideal pressure is. With the boiler off, the pressure will be lower than when it’s on, between 0.75 and 1.5 is normal.
Do I need to turn my boiler off to top it up?
It is not necessary to turn the boiler off to repressurise the system. You won’t have to switch off the power to it either. You will need to turn off the central heating, which can be done from the room thermostat, and let the system cool before filling it with more water.
When to check the boiler pressure
- When the boiler won’t start up.
- After bleeding a radiator.
- If you have any cold radiators.
- Before turning on the heating after a long time.
- Once a month during regular use.
What to do if the boiler regularly needs topping up
Having to regularly top up the boiler usually means there is a water leak somewhere in the system or the water pressure gauge may show reduced system pressure after bleeding a radiator.
You will need to investigate around the house for damp patches or leaks around radiators or check if drops of water are leaking down from the boiler itself. You may need to call in a gas engineer to fix the problem properly.
If you won’t be able to pay an unexpected expense such as a boiler repair, you could look to getting a repair plan from Hometree who offer customers peace of mind with home cover packages for their boiler, central heating, plumbing, drains and home electrics all at an affordable monthly or annual cost.
Do I need to top up my boiler every day?
It is not normal to top up a boiler every day, even if you have a small leak somewhere in the system. You should call a gas engineer to investigate as this could be a fault within the boiler.
Topping up the boiler once or twice a year is normal. We hope you have found this quick guide helpful but if you are not comfortable dealing with this type of boiler issue then please call a local gas engineer. Check out Hometree on our recommended page.
