old rads-hot ....new rads- cold

[tomfalconer]

As I am decorating my house I am replacing all the radiators.
The old rads were hot top to bottom.....now I am finding that the new more efficient ones are cold at the bottom and warm at the top.
Also three rads downstairs are virtually continuosly cold.
The system has been drained by a plumber..the rads have been bled..there is a new pump and a new boiler.
The gas board say there is sludge in the pipes and want to charge me the earth to force it through! Is there an easier option ?
And does anyone know if there system works.
Cheers.

 

[JohnD]

It might be sludge, or it might be that your new rads have a higher resistance to water flow than the old ones, so the hot water is taking the easy option and rushing through the old ones. to combat that, you turn down the lockshield valves on the hot rads to force more water to go through the others.

I presume you have already got your pump at full blast, and the valves at both ends of the new rads are fully open (especially if you've fitted thermostatic valves, as it's easy to do when you're changing rads).
It won't hurt to give the system a clean though. You can get a chemical cleaner, and (after you've rinsed it out) a corrosion inhibitor from your local DIY shed, or Screwfix is cheaper. just follow the instructions, One bottle will do an average house, up to 20 galls / 100 litres of water.
I had a British Gas powerflush when I had a hardened sludge blockage, bit provided the water is flowing in all rads, you can do it yourself. If you want to increase the flow in dirty rads to dislodge the muck, put the pump on full, and turn all the other rads off. That'll give a good blast in the open one. Give it a drain and rinse with clean water before adding the chemical, to get as much as you can out.

BTW it's not usual to get a lot of sludge in new rads, I'd expect the old ones to be worse, unless they've got narrower waterways.

 

[tomfalconer]

Hi John,
Many thanks for your reply.
All the rads have now been replaced thru' the house.
I have drained the system and put inhibitor in.
When i replaced the old rads there wasn't much dirt in them.
last night i turned all rads off ( both ends ) upstairs to try to force the heat downstairs..this wasn't very successful. Am i right in assuming that the rads downstairs should have then be piping hot!
Why did you have British Gas flush your system..did you know you had sludge ? did it work ?

 

[JohnD]

Why did you have British Gas flush your system..did you know you had sludge ? did it work ?

I have a BG maintenance contract on the system, after I'd had a rad off for repainting, I found the syst didn't refill. There was hardened sediment in the feed pipe. i couldn't track it down, called them in, they recommended a powerflush and said if I didn't accept their recommendation, they'd say it wasn't their fault if it went wrong again.

They also cut out and replaced the blocked section. I put Dearborn Benz inhibitor (and boiler silencer) which is the brand they recommend (I used to use fernox but it perishes the rubber in the 3-way valve) in when refilling, the syst seems pretty clean now, and on testing the water with a steel nail, it doesn't rust.

 

[tomfalconer]

I also have a BG maintenance contract on my system.
Maybe it would be a good idea to call them in.
I used Betz Dearborn Sentinel X100 Inhibitor last time I refilled system.Do they guarantee to improve your heating efficiency ?
Does it cost a lot ?

 

[JohnD]

last night i turned all rads off ( both ends ) upstairs to try to force the heat downstairs..this wasn't very successful.

I would have expected it to work... it would on mine.

How confident are you that the pump is pushing the water round? You should be able to feel it humming, and if you leave it off for a while, you should feel the pipes get hot as soon as you put the room stat on and the pump starts.

How old a house is it? in some old systems, there aren't two parallel pipes (flow and return) running all over the house, there's just one pipe and it goes in one end of each radiator, out the other end, then this (used) water is taken by pipe to the next rad. You haven't got one of these, have you?

I think I'm stumped!

 

[JohnD]

I also have a BG maintenance contract on my system.
Maybe it would be a good idea to call them in.
I used Betz Dearborn Sentinel X100 Inhibitor last time I refilled system.Do they guarantee to improve your heating efficiency ?
Does it cost a lot ?

Yes, call 'em in if you're stumped - that's what I did.

It wasn't very expensive at B&Q, but it's cheaper at screwfix. I kept a spare bottle in case of topping up after draining. It isn't supposed to improve efficiency, its supposed to stop corrosion.

 

[tomfalconer]

yes.... sorry to say I have one of the old one pipe systems ( noy very efficient I know ).... but everything was ok. when all the old rads were on!
I'll try the pump again and do what you recommend , but it's looking more likely that I'll be calling BG in....many thanks.

 

[fazal]

hi,
i have a similar problem with my one pipe system. The downstairs rads are cold except the very top and side 2 inches. The upstairs ones are only hot at the top half . The pump is on full and closing all but one rad doe snot help. I think its sludge in the system, and am planning to flush all the rads (at least the downstairs ones) an may replace some with new ones. I am worried that i will have the same probs that you have with your new ones. Did you manage to get the downstairs rads hot and how did you do it? Did you need a power flush or did you do it yourself with a hosepipe. Could one use a pressure washer to get more than mains water pressure?