how the hell does my (home) radiator work?

ok, background: just moved into a large (old) home, still has the boiler/old radiator thingys for heat. i’ve never used one of those things before, i don’t even know what they’re called. when we turned the gas on, about a day after i moved in, the guy lit the burner for the heat. and sometimes i’ll come home, and the radiator will be hot, so i turn the knob the other way, and it gradually gets cold…this has happened twice. now, it’s cold, and i can’t get it to heat up.


  1. am i dependant on the people below us, as in: do their radiators have to be on before we get heat on the second floor?

  2. does the heat automatically turn on when the temperature falls below a certain mark?

  3. does the heat work like every half hour? should i just leave the knob turned one way for a half hour and see if there’s eventually heat seeping out?
    these things (whatever they’re called) are a pain in the ass and should come with an instruction manual. HELP!


OK, I just got home from dinner and I had quite a bit to drink and I don’t know much about radiators. I’m not sure why I’m even responding to this and I’m not sure why anyone would still be reading after I admitted relative ignorance. In my defense I will say that I have lived in several places with steam radiator heat. I know what I used to do that seemed to work. This is the only help I can offer. I would imagine that someone with vast knowledge of the workings of boilers will come along soon to correct my mistakes but in the mean time maybe I can help you from freezing your tail off.

If I remember right there are actually two knobs on the radiator. One that looks like an outdoor hose spigot near the floor and another that looks king of like a big bullet. I think the spigot looking thing will turn off the steam completely from getting into your radiator and closing it will be like you don’t have a radiator at all. If this is what you closed I’d say open it and wait awhile. It isn’t going to make the radiator hot right away because it will take some time for the metal to get hot. The bullet looking thing is, I believe, called a regulator. It assists in regulating the pressure inside the system. If this is what you turned it could be that there isn’t enough pressure for the system to push steam to the upper floor of the house. Turn it back and wait.

I hope you have a warm and happy thanksgiving.

  1. Do you have a thermistat in your apartment ? If not, then you are at the mercy of whoever does.
  2. Yes, when the thermostat senses that the air temperature is too low it tells the furnace to turn on and start pumping hot water through the system of radiator pipes. The little knob on your radiator that you have been turning is the cutoff valve. It can be used to adjust the amount of hot water flowing through the radiator per minute when the furnace is on, or to completely turn off the radiator.
    3)The hot water gets pumped through the radiator whenever the thermistat tells the furnace to do so. You need to open the cutoff valve you have been playing with and leave it that way.

At last, one I can answer and one which caused me mucho grief in the finding out of.

Two main types of radiator systems, the older system which is used in large buildings - on this there is one flow pipe and all the radiators are connected to this one pipe.
Each radiator is teed off at either end so that it is in parallel to the flow, but the entry tee also has a baffle inside it which causes a small pressure drop across it, as you open your radiator valve hot some hot water tries to flow around the restriction(ie through the radiator) thus warming it up, the more you open the valve the greater the flow.The radiators are in series with each other.

On the other type of heating system, mostly domestic, there is a supply pipe from the boiler and a return pipe but the two are never directly joined.
Radiators are connected between the two and all the water flow passes through the radiators which are effectively in parallel with each other.

The problems of one part of the system being hot and the rest cold when the boiler and water pump are running are usually down to folk not understanding what the second valve on the radiator does - the lockshield.

There are a couple of things you do to correctly balance a system when it is new but once done it is rare to have to go through it all again,but one that does is in the case of people trying to get more heat out of their radiators by opening the lockshield valve fully.

Each radiators presents a resistance to the flow of fluid through it and it follows that the hot water will take the easiest route.The idea of the lockshield is to make sure that this resistance is equalised.If you open all of them up fully then all that happens is that you create a low resistance loop and all your hot water goes down one,maybe two radiators - a short circuit.

People often think that by opening both the main valve and lockshield valve fully they will get more heat but this is not true, one radiator will get hot, the others stay stone cold and, because the water does not give up enough heat on its passage through this truncated system, the boiler overheats the water(you can oftenh ear it just start to boil) and keeps cutting out on the boiler thermostat.

This is what you do - take a thermometer and go to the hottest radiator, measure the temperature at the inlet end and the outlet,(just hold the bulb to the pipe) there should be a drop of around 10degrees C, if it is less than that then the water is not giving it’s heat up properly - the flow through that radiator is too great.Close the lockshield down say halway and wait maybe ten minutes and compare the inlet and outlet temperatures, if the temperature drop is greater than the 10 or so degrees then open it a little.
Eventually you will get this radiator to its correct setting, now you go round all the other radiators and do the same.You actually end up having to go round several times because altering one radiator affects all the others a little but eventually you will come to a point of balance.

Ideally what you should do is to replace all the inlet valves with the thermostatic ones, that way each area will be maintained at the desired temperature, but this will only work on a balanced system.

It may be that someone else in the building, probably the ones closest to the boiler, is too hot and they turn it off or turn the electric thermostat down instead of turning their own radiators down.As I say it’s simply a case of a badly balanced system, in fact you should be able to run your system all year with the correct settings without turning it off as many folk do for the summer months, after all it should only come on when the temperature fall below comfort levels.