Trapped air in your pipes and radiators can cause problems such as unbalanced heating. It’s not always easy to locate the valves to release that trapped air. Not all radiators have a bleed valve on the side of the radiator. Some of the older styles have them on the back of the panel.
Check here first, if this is the case, you may need a special vent key such as the one shown below.
If there is nothing at the back, then you might have the scenario pictured below, where a plumber or engineer has carried out a repair and left a nipple where the vent should be.
If you are ever in doubt then call us for advice!