Bleeding radiators

Adly812

I have 7 radiators in my house. Only 4 I have on during the winter, as others are in rooms I don’t use. My radiators seem to be working, but I did notice two quite cold near the bottom and warm at top. From what I’ve read normally it’s the top cold when they need bled. 

I’ve lived there 5 years and never bled them before. Is it recommended to bleed them regularly or is it not a good idea if they don’t require it will it cause problems. If I bleed them, do I need to bleed them all even the unused ones? just wondering if I should bleed them anyhow given they’ve not been done for a while, and might be the reason why I noticed them a bit cold near the bottom.

grumbler

Adly812 said:

My radiators seem to be working, but I did notice two quite cold near the bottom and warm at top. From what I’ve read normally it’s the top cold when they need bled.

The only explanation I see is that the flow is so low, that hot water naturally goes to the top and the supply is too low to make the hole radiator warm.

mark_cycling00

I asked this question a while back. 
Advice was it's generally a good idea to bleed each year so things are in good working order. But the water pressure in the system and boiler will drop slightly so make sure you know where the water pressure gauge is on the boiler and how to top it up

The radiator in my bedroom never heated up, I bled it and now we have to turn it off on many nights.

Good luck 

stuart45

They might be sludged up. 

Adly812

stuart45 said:

They might be sludged up. 

I read that somewhere and considered it might need a flush of the system. It’s a Worcester 25i greenstar combi boiler. Serviced every year (5 years old). And flow is 60 for rads and 55 for hot water . 

YBR

stuart45 said:

They might be sludged up. 

We've experienced this with the lowest/last radiator. The grit and sludge from the system built up on one radiator leaving it cold at the bottom. The solution was to remove and empty the radiator and then add it back in. We may have had to do it twice, but not since.
I think my other half found instructions online.

Lorian

They may be sludged but perhaps  they haven't been balanced and the lock shield valves are too restrictive on the two with the issue.

ThisIsWeird

Your symptoms aren't of radiators requiring bleeding, as this would be indicated by having cold tops if anything.

Cold bottoms are generally caused by one of two things, as explained previously - one is a build up of sludge, which tends to occur in the middle-bottom of a rad, but this would show itself as a very obviously cold pyramid-shape in that area. That isn't what you have?

If it's a more general becoming-less-warm as you go down the radiator, then that's usually just an inadequate flow through the rad (say, system unbalanced), or the supply water is just not hot enough. Since you are only using around half the total number of rads, I wouldn't suspect a lack of flow in your case. (Bear in mind that all rads will likely be somewhat hotter at their tops - that's quite normal.)

A 60oC flow isn't 'ouch' hot, so I wouldn't be too surprised if the rads were a good number of degrees cooler lower down, and this would feel quite noticeable. If you are not happy with the heat coming out of them, try turning the CH output 5oC higher.

By all means also try bleeding the rads, but don't expect this to change anything, even if a small amount of air does come out. Make sure you know how to top up your system to ~1 bar again (if a sealed type).

You could also experiment by choosing one radiator and opening the lockshield valve an exact half turn more anticlockwise, and seeing if it heats up better without the other rads becoming cooler as a result. (An 'exact' half turn, so you can easily return it to its original setting easily once the experiment is over). If you find that this rad is now better, then by all means try opening the other three rad's LSs a half-turn too - see if they are all better. If they are, then you can conclude that the flows to the rads were too restrictive. If one rad (usually the one closest to the boiler) heats up far more than the others, then try closing that one off, say, a quarter-turn.

At all times, note their starting point so you can always return to this if needed.

Or, just turn the CH heat up 5oC or even ten, to see you though the cooler spells.

Or, wear more clothes :-)

FreeBear

ThisIsWeird said: You could also experiment by choosing one radiator and opening the lockshield valve an exact half turn more anticlockwise, and seeing if it heats up better without the other rads becoming cooler as a result. (An 'exact' half turn, so you can easily return it to its original setting easily once the experiment is over).

Use a permanent maker pen - Put a splodge of ink on the spindle and on the valve body, and then you have a reference point to reset the valve if a half turn is too much. I had a similar problem with a radiator that I balanced aiming for a 10-12°C drop between inlet & outlet. Only needed the tiniest of tweaks (in the order of an eighth of a turn) to get enough water flowing. Ended up with an 8°C drop.