Bleeding radiators!

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Posted: Fri Jan 26, 2007 3:52 pm

Ok, someone riddle me this:

I understand that when there is air in my central heating system, the radiator in the back bedroom, which I presume is the highest point, goes cold at the top, 'cos air is going to float on water, yes? I bleed the air out, and it all goes hot again.

Hayley pointed out this morning that the radiator in the front bedroom is cold at the bottom, and hot at the top.

WTF?

Mind you, I have been threatened with an African witch this week, maybe this is the first sign. Shocked

Posted: Fri Jan 26, 2007 3:57 pm

Heat rises, so maybe the radiator's not got trapped air, it's just operating inefficiently so it's not hot all over?

Posted: Fri Jan 26, 2007 5:27 pm

^^^^ Right. When a radiator is hot on top and cold on the bottom it means that there's air somewhere in the system and the circulation is insufficient.

It's hot at the top because that's where the warm water enters the radiator. It then doesn't get circulated properly.

Posted: Fri Jan 26, 2007 5:36 pm

Roycropper wrote:

Hayley pointed out this morning that the radiator in the front bedroom is cold at the bottom, and hot at the top.

sounds like the rad is sludged up, all the "gunk" in the system accumulating in one place.
You'll have to drain the system down, put some system cleaner in it and run it constantly for (IIRC) 48 hours, flush it through a couple of times then refill it and introduce some inhibitor.

If you have a header tank in the loft and a drain cock at the lowest point it's a piece of cake.

Posted: Fri Jan 26, 2007 5:38 pm

@KD you're wrong. cold at the bottom is sludge. cold at the top is air.
Also, most domestic rads in the UK have the pipework entering/leaving at the bottom.

Posted: Fri Jan 26, 2007 5:42 pm

Just found this here:

Quote:

Radiator cool at the bottom and hot at the top.
This may be the result of of a build up of "sludge" in the radiators and pipework. Iron oxide forms and is carried by the water around the system. The oxide collects and lies at the bottom of the radiator preventing the warm water from reaching it. To remedy this the radiator needs to be disconnected from the pipework and flushed through with water. You can also purchase sludge removal liquids which are added to the water in the radiators via the feed and expansion tank. It is usually left to flow around the system for a couple of days before draining the whole system down and refilling it with clean water.

I'd recommend doing the whole system, rather than a single rad though.

Posted: Fri Jan 26, 2007 5:47 pm

Yes the water goes in at the bottom. I kinda feared it may be gunked up. Hayley doesnt like the rad being on in the bedroom much, something we dont see eye to eye on. I cant understand why I pay good money to heat the house, yet we have to sleep in a cold bedroom.

Howsabout if I drain the system, take the rad off the wall and flush it through with a hosepipe, it works for car radiators?

Its gonna have to wait till this subzero spell finishes though.

Posted: Fri Jan 26, 2007 6:01 pm

That will work, but if you've got sludge in the system it's better, IMO, to flush the whole system and put fresh inhibitor in it.

I'll come round and do it for �150 plus expenses.

Master Baiter Joined: 15 Mar 2006 Posts: 193

I agree with Eamonn but also, do you have a thermostatic radiator valve fitted? These can cause a similar effect.
Its definately a circulation problem and most likely (though not necessarily) caused by sludge.
You can DIY it with some chemicals (fernox or centinel) lobbed into the system. method depends on type of system.
There's a bit more to it than that but if you want to try it, PM me and I'll give you a step by step.

Posted: Fri Jan 26, 2007 7:00 pm

No, I have the same radiators as the Flintstones. I suspect that because it has been turned off for so long it is full of rusty crap.

Plan A is take it off the wall and flush it, plan B fit a modern rad with a thermostatic valve. I'm not keen on sending the sludge and rust around the system, in case it blocks a pipe in a hard to get at/find place.

Master Baiter Joined: 15 Mar 2006 Posts: 193

Roy
Go with plan A to start with. Take it down the garden and flush it until its clear. Only experience can tell for sure but if its that old, replace it, they're not very expensive. Just don't go to the big sheds like B&Q et al use a proper plumbers merchant. They are about half the price there. Also, wear dirty clothes and look like a plumber and they'll give you even more off. Flashing your bum crack seems to do the trick Laughing

Posted: Fri Jan 26, 2007 7:20 pm

eamonn wrote:

@KD you're wrong. ...

In theory I may be wrong, but letting air out of my system made the radiators that were hot on top / cold on bottom hot all through.

Science loses. Razz

Master Baiter Joined: 15 Mar 2006 Posts: 193

@ KD
I'm sorry but I can't explain that one. But if you're sure and it works that's all that really matters.

Posted: Fri Jan 26, 2007 8:37 pm

excellent just solved my heating problem out.
one of my rads has a valve fitted so you can attach the hose pipe and let the water run out down the drain.

will sort mine out next week now i know the score.
2 rads out of 14 are warmish to touch the rest you cant get your hands on them.

Posted: Sat Jan 27, 2007 7:54 am

@RC

Just remember to cover all the carpet when you take that rad off the wall. The sludge is impossible to get out of carpet and you will always leave some water in the rad after you have drained the system

Posted: Sat Jan 27, 2007 11:41 am

@MM Don't worry, the rad is on Hayley's side of the bed, and I never see it. Very Happy

No youre right, I'll pull back the carpet and put something down. I aint doing it until it gets warmer though. I did try KD's 'defiance of science' approach, and tried to bleed it anyway, but as expected, the rad was full to the top with hot water.

Master Baiter Joined: 15 Mar 2006 Posts: 193

A tip Roy,
When you've emptied the rad, close the bleed nipple, bung the holes with rags & turn the whole thing upside down. Any sludge will then be kept in the rad. That stuff stains concrete like oil does so do it at the bottom of the garden.