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Help - radiator cold at bottom but hot at top

(18 Posts)
alexw Mon 14-Nov-11 13:15:10

Have had all radiators bled by BG when boiler serviced a couple of weeks ago. 2 radiators in sitting room not working properly - ie cold at bottom but hot at top. Any ideas for a solution gratefully received.

peasandbeans Mon 14-Nov-11 13:25:19

We had this problem. As far as I can remember the solution was something to do with topping up the water level somewhere in the boiler. In theory it was a problem that anybody could fix without calling an expert.

As you can guess I am totally untechnical, but I hope that gives you an idea of where to start looking for some more practical advice.

needtogetalife Mon 14-Nov-11 13:26:32

it needs bleeding, there is basically air in it. Do you have a radiator key?

moonstorm Mon 14-Nov-11 13:27:20

If the system is old, it could also be a build up of sludge. We had this problem, but it seems to have sorted itself.

Brownwolf Mon 14-Nov-11 13:30:34

you need to get a radiator key and bleed the radiator as there is still air in the system. you should be able to do this yourself, but if BG are supposed to have sorted it then they should come out again and sort it out.

AMumInScotland Mon 14-Nov-11 13:36:34

When radiators need bled, they are cold at the top and hot at the bottom - the opposite of what you have - so I don't think that bleeding them will be the answer.

Do you have a condensing boiler? They tend to have a round red thing nearby with a pressure dial on the front. If so, check the pressure reading - if its low then you should be able to sort it by putting more water into the system. There should be pipes and taps (like washing machine ones - just a quarter turn on a lever) which let water through.

noddyholder Mon 14-Nov-11 13:38:27

This is usually sludge. The reverse indicates air.There is a product called fernox(sp) that I think deals with this

inmysparetime Mon 14-Nov-11 13:43:04

Radiators that are cold at the bottom are full of sludge, especially if the cold patch extends higher in the middle of the radiator. You need to get them flushed to get the gunk out. There are two types of flush: chemical and power. Chemical flush is cheaper, they just put a bottle of chemicals in the system, leave it a day with the heating on, then neutralise it with another chemical. The risk with repeated chemical flushing is that it can corrode the radiators or pipework and cause a leak.
Power flushing is more expensive, and involves forcing water at high pressure and velocity through the system to unblock all the sludge. It makes an almighty mess, and if any pipes are corroded or weak, they will blow with the pressure.
What we did in the end was get new radiators, they're not that much really, compared to repeated flushing, and you'll have peace of mind.

Lottie4 Mon 14-Nov-11 14:10:33

If radiators are cold at the top they need bleeding for air, but if cold at the bottom there's a good chance it's sludge or small particles where the radiators sometimes rusts inside. If BG serviced your heating properly a couple of weeks ago, I'm surprised they didn't pick up on it then as any engineers I've had to service the boiler starts it up after it's been cleaned and checked and then checks the radiators are hot all over. I'd have a word with BG first to see what they say!

Our system was actually power flushed a couple of weeks ago when we had a new boiler. I wouldn't say it was messy at all as engineers had a special cover for the floor while they drained system down and connected the machine straight onto the pipework without a problem.

leeloo1 Mon 14-Nov-11 14:12:54

We had this and it was sludge. We solved it by draining the system, taking off the 3 worst radiators, taking them outside and running water through them with a hose - what came out was like treacle! Then when we re-filled the system we put a cleanser in - which I think needed draining, then an inhibitor was added. (From recollection re the chemicals - this was over 4 years ago and the radiators have been great ever since).

We did get a quote from British Gas before we did this and it was around £500 - plus, as inmysparetime mentioned, they mentioned the risk of radiators exploding! We have 'fancy' shaped to fit bay window radiators, so it wouldn't have been cheap or easy to replace them if they had needed to be.

Good luck with it - how we did it took most of a day - and a FIL who knew what he was doing - but it was quite satisfying. smile

alexw Mon 14-Nov-11 14:21:20

Thanks everyone. Will try phoning BG and explaining to them as they had serviced the system. Though I am tending to side weith the sludge theory...

PigletJohn Mon 14-Nov-11 16:27:05

What you are describing is caused by sludge. It is usually thick black sediment of iron oxide caused by the corrosion of the steel radiators. It is very common on old systems, especially if they are open vented and/or have not been treated with corrosion-inhibiting chemicals.

BG will tell you that you need a Powerflush, which will cost some hundreds of pounds. They will tell you that they are not responsible for your system being old and dirty, or for it not having been treated with chemicals. They will tell you that if you don't have it done, they will accept no responsibility for future sludge-related problems, and they will not be covered by any service contract. Servicing a boiler also does not include cleaning radiators. Sludge can block boilers, especially efficient modern ones.

An independent heating engineer will usually do a powerflush cheaper than British Gas, but it is essential to get a well-recommended one. In a typical house the job will take about half a day and involves a large machine with a powerful pump, and some aggressive cleaning chemicals. If you have a service contract, BG wil usually give a lifetime guarantee on their powerflushes, provided any piping faults are correct at the same time and you keep the corrosion inhibitor topped up.

If you or your DW are fond of DIY and can do basic plumbing, then you can do a pretty good job yourselves. You can buy a litre of Sentinel X400 for about £15 and give it four weeks to soften and break up the sediment, then drain it out with whatever has been loosened, then (preferably) take off all the radiators and hose them through in the garden. X400 is very suitable for DIY use as it is not acidic or aggressive and will not cause any damage. If in addition you can fit a Magnaclean or similar, it has a powerful magnet inside that will attract and trap any circulating black particles and prevent them causing future blockages. Magnacleans are spectacularly fast and effective, but BG no longer fit them as they tend to leak after a while. They have a 2 year guarantee and by that time they should have captured all loose aprticles in your system, so you could just have it removed then. Other devices are available but none are as spectacular in use.

On final fill after cleaning, be sure to add a litre of X100 or similar to prevent future corrosion.

Note that corrosion inhibitor chemicals are NOT cleaners, although the same companies usually make both, so adding an inhibitor will not clean out existing sludge.

ukhomecare Tue 28-Oct-14 13:48:39

Message deleted by MNHQ. Here's a link to our Talk Guidelines.

Thomas48 Sun 14-Feb-16 19:26:58

In most cases some of the time the vales on your radiator is not letting more hot water into your radiator try Turing the vale to close for a bit until the radiator as gone cold then open the valve if the radiator dose not get hot all over or any part of the radiator it's the valve needs changing

oliverp Mon 23-Jan-17 10:15:55

I have had my radiators power flushed, because some radiators were cool at the bottom and I understood that this is caused by sludge. I have now checked them all, and half of them are cool at the bottom. The plumber says that is normal. Is he right? Is there an adjustment to the conventional boiler to make the radiators hot throughout?

Darkwater Tue 24-Jan-17 19:49:39

Oliverp your plumber is full of sludge for telling u that. If u have a heat only boiler and hot water cylinder , the cold rads could be due to a faulty central heating pump. If u have a combi turn your hot rads off at the valves (TRV and end shield) see if the cold areas become hot , if they do and have no cold spots at all , turn the others back on and see if they stay hot.

oliverp Tue 24-Jan-17 23:42:51

Thank you Darkwood for your post. I have a boiler and hot water cylinder. What could be wrong with the pump, when half of the radiators are working fine? I will try turning the hot radiators off to see what effect it has on the poor ones.

Darkwater Wed 25-Jan-17 08:19:31

The central heating pump can become less efficient with time , check its speed setting . Normally they r set to 2 , if so knock it up to 3 and c if it makes a difference.

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