Noisy radiator and too much water when air is let out

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One of my radiators is noisy, a water-bubbling noise. It's a modern radiator in the bathroom, cased, with two valves - one on the top right corner, and the other on the bottom left, it only works when both are open, not sure if that's what supposed to happen. There is a screw on the top left corner (above one of the valve, i.e. same side) - I've been told that's where you unscrew the bolt to bleed the radiator. So when it was done a few weeks ago, the air came out and a bit of dirty water (very small amount). Since then the noise didn;t stop for more than a couple of hours straight after.
I've now unscrewed the bolt again (second time since the initial bleed) and a LOT of air and water comes out - I filled a 1.5l bottle and more was still coming but I screwed it back off as I'm worried it's wrong. Watre comes out from the same place as air by the screw in a steady strong spray but also sometimes there's smell of gas while it does and the water is slightly foamy in the bottle.
Any advice please? I hope it's not dangerous as it seems like some gas is coming out. Is this the right way to bleed it?

My bathroom rad does this if the system pressure falls too low.

If your heating system is a sealed system you need to find the inlet valve somewhere near pump that allows more water into the system. Dont let anymore water out. You are making it worse.

is there a pressure gauge on your boiler?

When you bleed a radiator you should turn the boiler fully off so the pump is not running.

heck, I didn't know I needed to turn off the boiler! I've seen many times it being done (not in this house) and can't remember anyone turning boiler off.

Beta, where to look for the inlet valve? on the rad itself? you mean asme as Pigletjohn, near the boiler's pump? and what does that look like?

The think is, it's my gardener who said that's how you do it and he never mentioned turning anything off (though actual heating was off as it's on thermostat at the time I was doing it - isn't that enough?)

I thought that i may be making it worse this time - I've switched off the rad (valves) for now.

thing, not think - sorry I'm now panicking so can't type!

I'm pretty sure there is pressure gauge - there are a lot of various dials on boiler, it's about 10yrs old. I think it's the one with 0 and 1 on it -arrow's on 1.

there is, not 'are' (argh!)

other rads are fine hough, so not sure it's the pressure?

is there a pressure gauge on your boiler?

If it has a pressure gauge, then it will have a pipe and valve to repressurise it.

Have a look for the instruction book tomorrow.

Is it your own house, or rented?

When is it next due a service?

own house, I'm really not keen to pay for the servicing right now, expenses too high this coming month. it's due soon if you mean a yearly service.

CAn you advise how to correctly let the air out , Piglet? I want to do this myself if I can. I described above what I think is pressure gauge but as I say, lots of dials. Not sure I want to alter anything on boiler, it's been set about a year ago during servicing and if I change anything then all rads could go haywire. It's only one that is a problem, thoulg one rad downstairs makes loud knocking sounds when it comes on but it only lasts a few minutes so no big deal, maybe something else entirely. The noisy bathroom one is important as I like it to be on at night and it's next to the bedroom.

just to add that this is a new problem, maybe about 5 weeks.

if you bleed it, the pressure will go down and you will need to find the pipe and valve to top it up. Bleeding is easy. If the water is white and foamy it is probably the corrosion inhibiting chemical that is added to the water. However if it is black that is a sign of corrosion in the radiators, which also causes gas to be released. This is more common on radiators that are old.

If your radiators have a chrome nut, they are probably newer than if they have a small screw-in pin.

I mean that next time it is serviced you can ask for instructions on topping it up (write them down and take photos).

Post some pics of the boiler and the pipes around and underneath it, and coming out of the top, also of the (possible) pressure valve which should be marked in Bar. About 1.5 is about right, but not lower than 1.

p.s.

if the top of the radiator is cold, that is because the hot water does not reach the top, so it has air or gas in. If the top is hot, no need to bleed.

If the middle is cold, it has sludge.

I will try t opost pics later this week as not at home today.
It's hot pretty much evenly- it had a cold corner but after 'bleeding' it's fine. it's the small screw on mine. Did the air cause the noise though - and then I made it worse by letting so much water out? Should I keep it off for now or is it safe to have it on? I still don't see what is the reason for the noise and water coming out - the pressure was unchanged for a year and it's only this one.
Thanks Piglet.

it might be the first radiator on the circuit from the boiler. There is often one that collects more gas than the others.

You do not need to leave it turned off.

The noise might be because water is pumping through it too fast. If one of the radiator valves is thermostatic, adjust the other. If not, adjust the one without a knob. If they are identical, adjust the lower one. Turn it fully closed, them open half a turn only. Turn on the heating, go away and do something else. After half an hour, feel the pipes coming out of both the valves. One of them should be "too hot to hold" and the other should be hot like a teacup or a hot tap, so not scalding. If it is cooler than that, open the lower valve another quarter turn and leave it running another half hour. Almost all the adjustment is in the first turn or two from fully closed. The idea is that the water should flow through the radiator slowly enough to lose about 20C of its heat. The lockshield valve should not be fully open on any radiator, its purpose is not to turn on and off, but to regulate the flow. If you do not have thermostatic radiator valves, you can adjust the lockshields so all the rooms heat up to the right temperature, rather than some getting hot too fast and others being too cool. It takes a while to do that, so try not to lose the adjustment by turning them fully on or fully off. You can use the valve with the knob to do that. A lockshield valve usually has a small plastic cover on the spindle to prevent people fiddling with it, but a spare knob or a very small adjustable spanner will turn it for adjustment.

thank you Piglet, will try that.

thanks Piglet, it seems to have worked - not completely silent but much quieter! I did suspect that both valves should not be open fully but didn't know what exactly to do.

Slight issue with another radiator - warm on top half and coldish on the whole of bottom half. Is it air? CAn I just let 'bleed' it by unscrewing the top corner thing, while it's off (valve) as I don't want to fiddle with the boiler?

Cold at the bottom is insufficient flow. Turn the others off. Does it warm up all over, or is it cold in the middle?

It does not need bleeding if the top is hot.