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can you ELI5 the physics of bleeding radiators on an apartment building?

I live on the 14th floor of a 30 story apartment building and so far, I’ve been bleeding my radiators myself.

This usually worked and after bleeding I had a fully functioning radiator, 100% filled with water.

However, last time I tried bleeding, it would only fill up to 25% of its volume, it’s like there’s no pressure in the circuit.

Am I doing something wrong?

ContrarianTrail , (edited )

Plumber here.

It’s a closed circuit. When you’re bleeding out air the pressure in the system drops. When there’s no sufficient pressure the water wont reach the upper floors.

Under normal circumstances the system is bled of air once and then they add more water untill the optimal pressure is reached and that’s it. You shouldn’t need to bleed air or add water ever again. The fact that you keep bleeding it indicates that new air is introduced somehow. Usually this means there’s a leak and someone keeps topping it up with fresh water which contains air that then need to be bled out again.

Alternatively the issue could also be non-plumbers like yourself who keep bleeding the radiators on their own and then the maintenance keeps adding more water and wondering why the pressure always drops again. In my part of the world it’s forbidden for the residents to bleed their radiators for this very reason.

Also, the radiator lines are usually steel. The reason they don’t rust is lack of oxygen. Now with constantly more water and thus air being added to the system the corrosion keeps on advancing.

BearOfaTime , (edited )

How do you know how much it’s filled?

Also, hot water heat works differently than steam, and many steam systems have been converted to hot water, so it’s not easy to know just by looking at a radiator.

As other people have said, let the maintenance folks handle it. They know the system.

bluGill ,

There needs to be space someplace in the system since water expands when it warms. Sometimes that space is in the radiators andso bleeding needs to not let all the air out, for this reason you should get maintenance toefix the problem if one exists so they can balance the system.

ContrarianTrail ,

That’s what expansion tanks are for. There shouldn’t be any air in the system itself.

HubertManne ,

I have only done it with steam type and honestly I felt it was one of those more art than science things. buying the adjustable valves was nice to control temp a bit.

rockSlayer ,

Having lived in a house with radiators, bleeding registers is like a once every 5 years type of task. There’s a much larger leak in the system, you should talk to your apartment manager.

nous ,

A water central heating system is a closed loop system that is under pressure. This means the water in it is circulated around and around the system and is cut off from other water supplies under normal operation. Naturally, slow leaks happen and gas can enter the system in various ways so occasionally this needs to be released from the system. Any gas in the system naturally collects at the highest points along the path - which tend to be the radiators.

When you bleed a radiator you are opening the system to the outside and hopefully where the gas has accumulated. Since the system is under pressure it forces the gas out of the system to equalize the pressure with the outside. This will cause the pressure of the system to drop and eventually it will stop.

However there should be a control valve somewhere, typically on/near the boiler that connects the central heating system up to the mains water supply. You can open this valve to cause water to flow into the central heating system and pressurize it and really this should be done every time you bleed the radiator a significant amount.

In apartments though you might find that you are on a building wide circuit, or you might have one isolated for your apartment. If you have a boiler in your apartment then you are likely on a closed system and should be able to equalize the pressure yourself. If it is building wide you need to talk with your building manager.

Note that you should not need to bleed your radiators that often. Once every several years should be more than enough. If you are doing it frequently then you likely have a large leak in your system and likely want to get someone to check that out.

ODuffer ,
@ODuffer@lemmy.world avatar

Great answer, there should also be a pressure gauge somewhere on the boiler. As mentioned, this is really for your building manager though.

bstix ,

That depends entirely on how the system is set up. I would only ever consider increasing the amount of water in the system if I was absolutely certain that my apartment was on a completely separate and closed circuit than the other apartments. You should contact the janitor or whatever it’s called.

Successful_Try543 , (edited )

Usually, at the heating boiler, there is a junction for a hose with a valve and close by a pressure meter. If the pressure is too low, the janitor (not you) should fill up the heating system with water until the pressure is sufficient. Ideally, the pressure should be checked again after bleeding the radiators.

bstix ,

Yup, that’s how it’s done when there’s a heat exchanger.

However there’s a reason why the boiler room is usually locked off in a 30 story building. Bleeding a radiator might be relatively harmless, but there’s no way of knowing what the pressure is supposed to be without knowing the entire system.

Some (lower) buildings might even have direct district heating without an exchanger, which is absolutely no go to even bleed.

vk6flab ,
@vk6flab@lemmy.radio avatar

I’d expect that the person to ask would be the building manager.

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