Bleeding radiators - turn off boiler or put on frost setting?

[Minnimoomin]

So it's finally time to bleed my radiators for the first time. Sorry if this is a noddy question, but do I need to fully turn off the boiler, or do I turn the thermostat to the frost setting?

I dont adjust any settings tbh
Are your radiators cold at the top when they're on? That's the only time I bleed mine

Yes do it when the radiators are off. I don't think you need to turn the dial to frost setting or turn the boiler off though.

You don't need to do anything, you just bleed them. Do they actually need bled? It's not a routine task like washing windows. Usually, in my experience, there might be one radiator every so often that needs bled but never them all.

Thanks for replying. Yes, they're cold at the top and I'm having to whack the tjermostat up to 23 to get the rooms decently heated. I've read you're meant to switch the boiler off before bleeding the rads, but my thinking is that if the goal is to cool the water in the system, the frost setting should do it?

I do them when the heating is on. Because that's when the water will move around. Be careful because it's hot water that will leak out. Have a tea towel/cloth ready. Do it slowly and with patience.
In my old house it was a regular task. Here I've only done a couple in 5 years.

I don't switch anything. I just slightly loosen the valve on the radiator to let the air out, holding a rag under the valve to catch any dirty water.

I also do it when the heating is on (BIL is a plumber/gas engineer) they only say to turn it off so you don’t risk scalding yourself if any water shoots out of the radiators, but I’ve never had that happen in over 30 years of doing it.

Yes Hutton it down a couple of degrees below the point where it clicks in. You are not supposed to bleed hot radiators in case you get burn

Thanks. I was overthinking it, evidently.

I find it easier to bleed when the heating is off. Start at the bottom of the house and work up. Remember to check your boiler pressure is over 1 after- if not you will need to repressurise the boiler

I've always bled the radiators while the heating is on. Never thought to do it any other way.

I'm not a plumber, but I'd thought you need to make sure the heating system is above 1 bar before you can bleed rads to get rid of air. If the pressure is below that bleeding would suck more air in?

I usually have a jug ready for the water that comes out.

God I love Mumsnet sometimes.

Plumbers: Turn the boiler off at the mains and wait till the radiators are cold.

MN: Turn it down a bit, mind you don't burn yourself.

😆

Thanks all.

I do it when the heating is on.

You need to put a container under the tap to catch the water and obviously be careful not to spray yourself with hot liquid.

Also, check the pressure before you start to bleed, because as you bleed the pressure will decrease and the boiler may stop working, and remember to top the pressure up after you have bled if it has gone down, or else the boiler won't work.

I blew my old boiler up bleeding radiators while it was switched on. I bled the radiators, the pressure dropped below the threshold, the interlock should have kicked in fine and stopped it, but instead the main pcb blew up and the boiler was toast. Of course what should have happened is that the interlock should have kicked in fine and just stopped the boiler working rather than the boiler deciding to destroy itself. I suppose that is the kind of thing that happens when you switch in circuits that haven't been used for 10 years.

We just turn the thermostat down so the heating is not running while they are being done

If you have a lot of air come out check the pressure again you may need to re-pressurise. I usually check pressure after each radiator if there's a lot of air. A bit of running up and down, or someone watching it for you. Open the tap nice and slowly until you hear the air hissing or see water starting to drip, close quickly when the water starts to drip, don't open the tap further than necessary.

Is is only certain types of boiler that have the pressure issue? I've had at least 3 boilers over the past 40 years, and never once had pressure been mentioned in relation to any of them.

Thanks for the reminder about the pressure issue, I had seen that.

I think it is only combi boilers not traditional boilers (separate hot water tank).

I have a hot water tank system (system boiler) and the heating loop is pressurised.

Maybe wrong but I thought they all are nowadays.

My system is v old, so you could be right!

I've never had to do anything with pressure and don't have a pressure gauge on my boiler. I have a conventional boiler with water tanks in the loft and a hot water cylinder

Thanks @IClaudine and @dementedpixie . That's the sort of system have always had and no one has ever mentioned pressure so that's reassuring 😁