Any heating engineers in the house?

Is there a specific method to draining air from ch radiators? Is it best to start with the highest radiator in the system and work down or other way round?

Do they all need bleeding?

Generally it will be the upstairs ones that need bleeding and the one in particular which is the highest. We have an upstanding/towel rail one in our bathroom and that one is usually the only one with air in it.
You can also tell if individual ones need bleeding by feeling the temp diff at the top and bottom. If it needs bleeding the bottom will be a lot hotter than the top.

It’s not air, it’s hydrogen from the oxidation of the insides of your steel radiators. If a lot is collecting you need to add more inhibitor to the system, which is basically an alkali that reduces the acidity and hence the corrosiveness of the water.

It could be air, especially in pressurised systems which take top-up water direct from the mains. The heated water degasses over time.

You can check which it is: hold a lighter close to the gas comeing our of the bleed valve when you open it. Hydrogen burns with a visible flame.

I hope globalti is talking rubbish. Last/highest one on a loop worked for us (though I did them all, only two had air in), had two rads basically empty and system working much better after bleeding.

Globalti is right. Its degradation and corrosion . We have had our heating system flushed and cleaned, new boiler, inhibitor etc and this is now year 2 of no bleeding of rads……….

If the thin metal of a radiator was sufficient to keep hydrogen contained wouldn’t we all be driving hydrogen cars by now?

That’s why you have a feed and expansion tank in the loft or an expansion vessel in the boiler to keep the pressure build up to a minimum

OP lots of detailed answers here, I think the most important thing is to have an old towel to make use no rusty water goes onto the floor carpet 😉 . Yes start at the top and work your way down the house, in my experience you can tell which radiators need bleeding as the top part is cold/cooler (where there is trapped air) whilst the bottom part is hot.

‘s not air, it’s hydrogen

Where’s my splint, how loud a squeaky pop can I do?

Try it AA and report back…….. What could possibly go wrong? 😯

Top tip, make sure the pump’s off before you start. Don’t do what I was doing for months and bleed air into the system… 😳

He’s right it is hydrogen

lol

Great advise. Thanks all.

AA, thought I felt the ground shake 😯

Chuckled out loud at that ^^^ pic. 🙂

bleeding rads.. the guide..

make sure central heating is off and rads are cold.. start at the the lowest rad and vent till water exiting is bubble free.. repeat on every rad leaving the highest vent point till last usually the bathroom rad . simples..

no water from rad.. problem. black water from rad.. problem building up. clear water from rad.. happy days..

do not ever close rads off ever .. if you must leave them just cracked open but never turn them off completly the lack of circulating water will allow deposits to build up very quickly and cause you problems..

do not ever close rads off ever .. if you must leave them just cracked open but never turn them off completely the lack of circulating water will allow deposits to build up very quickly and cause you problems..

This is a new one on me but makes sense. My mother is living in a house that is far too big for her and can’t afford to heat (long story, but not something she can do much about for the moment). She currently has radiators turned off in 6 rooms. Does the frost protection setting most rad thermostats have on them equate to just cracked open?

I was bleeding the radiators in her house yesterday as it happens – some of them are weird, the whole front panel was cold and the back hot but a tiny bleed (like less than a second) of air was sufficient for the whole front to immediately become hot, almost like a little air pocket was preventing air from reaching a whole panel.

Turning a radiator off entirely won’t cause it to magically fill with limescale / sediment / other deposits. Provided there’s inhibitor in the water it won’t do any harm at all. What do suffer from never being touched are thermostatic radiator valves, which really need exercising once a month or so.

If you’re concerned about inhibitor levels then dump one of the pressurised cans of Fernox into the filling loop.

I hate thermostatic radiator valves – I am sure I have spent more money replacing them than they have ever saved in heating bills.

Theres issues with your water if you are replacing them regulary. I have replaced my Wickes own brands after 10 years service after flushing our system and fitting a new boiler with Drayton ones. If they are sticking or leaking, could be sediment and muck causing this rather than a valve fault.
You can change them without draining a system down on an open system, by using bungs in the f&e tank. Takes 20 mins and you loose a mug of water, so not time consuming, if that’s the issue with the costs.

Drunken memories of bleeding a hot combi system, and over undoing the bleed nipple and having hot jets of water shooting across the room, wallpaper and tv…..bleeding while drunk not recommended.

bleeding while drunk not recommended.

We’ve all been there.

The rad in our spare room was cold about 60% of the way down the back panel – I tried bleeding it and got nothing – zip – nada. I eventually figured out hat even though I had the valve “stem” in my hand that the valve itself was blocked. Luckilly our rads arethe type where the whole valve can be unscrewed so I got the air out that way. It’s fixed the noisy and troublesome cavitation sounds we wqwre getting at the TRV in our bedroom 🙂

make sure your system pressure is topped up before and after doing a bleed- if you have a lot of bleeding to do – maybe check after the first few radiators.