Loss of Pressure in Your System
For a system to work properly the water pressure should remain constant. Modern combination boilers are pressurised systems and water will enter the system from the mains cold water supply through a manual filling device, known as a 'filling loop'. Adding water via the filling loop to the system after a drop of pressure will help bring your system to the correct pressure again.
There are several factors which may contribute to a loss of pressure in your heating system. It could be as a result of a water leak or air removed from the system when the radiators have been bled or removed and replaced. You should check the pressure after bleeding or removing the radiators and if you notice a drop of pressure then the system will need to be topped up with water.
Water leaks will also cause a drop of pressure, leaks can be very small and go unnoticed as pressure can decrease over a couple of months. Small leaks are quite hard to detect as the water evaporates quickly. If you think there is a leak, you should check the system thoroughly when it is cold especially around the radiator and boiler valves. Larger leaks will mean that you will need to regularly refill the system; these should be repaired as soon as possible.
You can check the pressure of the system by using the pressure gauge which you should find on your boiler. You should check this gauge regularly to make sure it is at the correct pressure. It should be between 1 and 1.5 bar. It should not drop below 0.5 or rise above 2.5.
If the pressure is too low then you need to re-pressurise the system by topping it up via the filling loop. This is usually a small tap connected to the system via a metal hose. If the hose is not connected to the system you will need to remove the cap the end and attach and tighten it. Once attached, you need to turn the tap, whilst watching the gauge and let enough water in to raise the guage to the correct level (1-1.5bar).
The filling loop will always be located near to the boiler but if you can't see it straight away it may be in a cupboard or perhaps behind a boarded section. If you cannot find the filling loop, consult your manufacturer's booklet or ask your service engineer.
copied & pasted, but somehow I don't think it will be much use to you, however you will heat up when you scream, "I've already tried that dummy!"
