Read the gauge before anything else
Find the pressure gauge or display on the front of the boiler. Most domestic systems are designed to sit at roughly 1 to 1.5 bar when the system is cold. It is normal for the needle to rise a little as the heating runs and the water expands. If it is sitting below about 1 bar cold, the boiler may lock out or refuse to fire, and a top-up is the first thing to try.
One reassurance: a slow pressure drop over many months is normal life with a sealed heating system, often just from bleeding radiators or tiny seepage. A drop you can watch happening week after week is a different story, and that difference decides everything below.
Topping it back up yourself
Repressurising is normal homeowner territory and your boiler manual shows the exact method for your model, so check it first. The short version: with the boiler off, find the filling loop, usually a braided silver hose or a built-in lever under the boiler, open it slowly until the gauge climbs to around 1.2 bar, then close it fully. Do not walk away with the loop open, and do not chase a higher number, because overfilled systems just dump the excess through the relief valve outside.
If radiators have cold spots at the top afterwards, bleed them with a radiator key and expect the pressure to dip slightly, then top up again to the same mark. If that routine holds for months at a time, you are fine, and a yearly check at service time keeps it that way.
When to stop and call a professional
Call a Gas Safe registered engineer if the pressure drops again within days of a top-up, if you can see water anywhere it should not be, under the boiler, around radiator valves, or staining on ceilings below pipe runs, or if the small copper pipe that exits through your outside wall is dripping, which usually means the expansion vessel or relief valve needs attention. Repeated lockouts with error codes are also a fault, not a top-up problem.
The honest reason not to keep topping up forever: the fresh water you keep adding carries oxygen and minerals that corrode the system from the inside. Finding a leak early is cheap. Replacing rotted radiators or a heat exchanger is not. If you are local to Bridgend or the surrounding county, call Lloyd on 07712 646488 and describe what you are seeing, and you will get a straight answer about whether it needs a visit.
