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I have 3 radiators that seem to get hot (more like warm) at the top but cold at the bottom. They are the 3 furthest from the boiler. They are nearly 25 years old, but no sign of outward deterioration. The boiler is not an issue - It was replaced 12 years ago and is plenty big enough for the property. Over the years we have tried bleeding and balancing, but those 3 radiators remain problematic. Each rad has a therostat, which works (I've checked for sticky pins etc). I have a Magnaclean installed, which is regularly serviced and pulls out 'normal' levels of gunk.

Internet tells me that the symptoms are a sign of sludge or debris in the system. The remedy being either a power flush or replace radiators, which allegedly have a life span of 15-20 years. I've been quoted over £600 for a power flush, which Google suggests is ballpark (between £350-800 depending on size of system). It also suggests doing it every 5 years (which I haven't done over the last 12 years). I was thinking that this was expensive, and it might be better to put that money towards just replacing the radiators.

Is this anyone's field of expertise or does anyone have any experience and (relevant  ;) ) advice they could offer please?

I would ask a reliable plumber for his opinion and get quotes for new radiators and a power flush to see which is more viable.

The 'reliable' bit is the difficult bit. I have the one quote from a company that favoured the power flush, but I'm not 100% convinced. I fear spending that money and ending up having to change the radiators anyway. But, I might be overthinking this.

Not sure whereabouts you are but there’s a few decent plumbers I know of in Swindon.

Only my experience but I had an old system and had a power flush which made no difference. Some plumbers will take Rads off and clean them out. So I would go for that or new Rads given their age.

I had new radiators througout the house in 2023 and new pipes fitted too. In all fairness I think most of the radiators had been in the house since the 70's/80's and the same with the pipework, and the plumber (who is a family friend) showed me some of the old pipework and it was full of sludge.

Had no problems since it was done, all radiators piping hot when i want them to be. Before some were luke warm at best (due to the sludge).

So i would go for new radiators and make sure the pipework doesn't need replacing too as they did in my house.

We had a really old radiator in our bedroom that was doing the same thing. Got a new one and its like a totally new room in the cold winter months. I think when they get to 25 years old it's probably most as well to replace them.

Have you tried bleeding them?

Had ours replaced not too long ago, surprised the difference it made and I was surprised how cheap the new radiators where, personally wouldn’t waste my time and money messing about, just get new fitted, job done.

Yes, no difference.

Sorry chaps, missed all of these answers!

I think I reached the same conclusion as you - Change the radiators!

Thanks all.

You can remove each radiator. Take them outside and flush it with a hosepipe. That will remove sludge

If you close down all the other radiators do those three get hot?

If they're furthest away, it could be a balancing issue or the pump struggling.

What Sam said, we had the exact same issue. Took the plumber 5 mins to balance the system and all was good.

Tried the balancing thing a while ago and no difference.