One of my radiators isn’t working: it’s full of water but the water is cold. The building I live in (I’m on the 3rd floor) has communal heating and uses an old oil boiler but currently a new gas boiler is being installed and while this happens a temporary boiler has been put in. The temp boiler is up and running now. I asked the on site plumber about my radiator and he said if it has water in it then it is not a problem with the boiler but probably means the valve in the radiator needs fixing. Does this sound right? – ( I would have thought the water came up hot from the boiler …?). Confused as the radiator was working last winter.
Also, another of my radiators (which is old – 1930s) is hardly giving out any heat – some of the water than came out when I bled it was black; does this mean it is blocked by sludge? I have been advised to have my radiators cleaned. Is this really expensive?