I don't know if it's different from the radiators in Germany, but here the plumbing is all taken care of (and in my flat I can hear the water start flowing into the bathroom radiator, proceed into the bedroom and living room, and then out into the kitchen) and you shouldn't loosen any nuts at all, as that's how the repair people drain them before repairing them.

Don't you live with a guy who has lived in England for a bit and can tell you if things will blow up if you don't do something?

Huh, I always thought they were filled when they were made. Is the manufacturer's name on it? If so, try their website.

The radiator is part of a central heating system that is linked to the boiler. It's a sealed system of pipes and radiators that run in a circuit.

There should be a little valve somewhere on the boiler (not the radiator) that allows the system to be filled up with water from the mains.

By letting water out of the radiator, you'll create an air lock in the system. It won't harm it, but the boiler will need to be 'topped up' at some point and the air lock released. That's why there is the key, to let air out of the system (not water). Also, some central heating systems have anti-scale stuff added, and by letting water out of the system you'll dilute it when it's refilled again.

What type of boiler is it? Is it one where the boiler fires up and the water heats up as soon as you turn the tap on (a combi-boiler, common in flats) or is there a separate hot water tank in a cupboard somewhere that heats up the water?

Leave the key alone. Just back away now.

Oh yeah, the central boiler will have a little water gauge on it, and that's what you fill up (mine has a faucet connected to a hose that runs into it to do the filling. It's pretty self-explanatory). If it goes empty - no heat for you and the man who comes by once a year to make sure it's functioning properly will give you a lecture about how you need to keep it filled between 1/2 and 3/4.

The radiators are not filled when they are made. They are hollow, and only when the installation is completed with the circuit of pipes and radiators linked to the boiler is the system filled with water (and anti-scale).

Letting a little spray of water out of one radiator will not harm it, but if that happens regularly without the system being topped up, it'll stop working and you might end up damaging the boiler, which will be way spendy to fix.

Hey Specklet!

How's it going over there, anyway?

Specklet said that this is a towel rack.

If your boiler has a pressure gauge, there'll be a tap or a pair of taps on the bottom of to let more water into the system. You want the needle somewhere in the middle. If there's no pressure gauge, you don't need to do this.

The valve you played with is to let the air out of the system, which collects at the top of every radiator (including the towel rail). Every so often (annually or monthly or weekly, depending on the crumminess of your plumbing) you need to go around and undo each valve until the moment water comes out.

Okay, thanks, I'll check the boiler. We don't use it, though, the only hot water in the flat is in the shower, and that's heated as you use it, not by the boiler.

Seems like it's fine to use.

cmonkey, the English guy doesn't know anything about how it works, and has never used it.

It'll be something like this, that's part of the central heating system. I have one, it's just another radiator on the central heating circuit, but designed in such a way you can hang towels over it.

It's not part of the central heating system - I noes this because there isn't one :) *insert whinge about storage heaters here*. It's a standalone thing that, as Specklet said, I never turned on before she got here. So, er, yeah.

Stop playing with things you don't understand ;-)

I think you will find it is filled with water to store the heat better after you turn it off, probably through the nut you loosened. If you let too much out you may have to refill it, but a tiny amount probably won't matter much.