Low risk
Feel both pipes into the cold radiator. If they are hot, hot water is arriving and something inside or at the valve is stopping it. Check the valve pin, then the lockshield, then bleed it.
If the heating is off but radiators are hot, hot water is still reaching them. That is usually a stuck valve, a hot water schedule or a frost routine.
Air rises, so upstairs is where it collects. Bleed the top floor with the heating off, check the pressure, then look at balancing.
Caution
A drip from the spindle is usually a worn seal or a loose gland nut. Tightening the gland a quarter turn often stops it. If not, the valve needs repacking or replacing.
Air that keeps coming back is entering somewhere. Note the boiler pressure over a week: falling means a leak, steady points to corrosion or a vent.
Take off the valve head and press the pin underneath. If it does not spring back, it is stuck. Freeing it or fitting a new head often fixes it.
Ticking and creaking as the heating warms up or cools is usually pipes moving on their clips or the floor. It is harmless and can be quietened.
A water-filled towel rail that is cold at the top is full of air: bleed it. A rail that is only hot when the hot water is heating, or never in summer, is usually on a different circuit.
Describe the job and get a fixed price from a local heating engineer.
