Two cold radiators, rest fine, balancing doesn't seem to help

[Ytee2]

Hi everyone,

I have CH with a system boiler with a header tank and 8mm micro bore pipes to the radiators, fairly standard setup I guess. House is 1990s.

My issue is that two of my radiators are cold, while the rest are perfectly fine. Both the problem radiators are downstairs and close together, on either side of the same wall. One in the lounge and one in what was originally the dining room. Previously, only one radiator was cold, the other was ok. But since I had some TRVs fitted recently and the system was drained/refilled, neither has worked.

The plumber told me that it must be a sludge/blockage issue, and advised me to pay him to do a Powerflush. I'm ok with that in principle, but I want to be sure that's the right thing to do first.

Here's what I've tried so far:

• Tested on all available CH pump speeds. The pump is fairly new anyway and feeds all the other radiators fine even on minimum speed.
• Turned all the lock shields off except for one of the cold radiators at a time and ran the pump on max. The pipe and valve gets hot but the rad doesn't.
• Opened the drain valve on each radiator one at a time to see how fast water was released. Compared this with one of the 'good' radiators. The water flow is about half the rate from the cold radiators as from the good one. Noticed that the cold radiators actually get warm during this process, but go cold again afterwards?? Don't get why.

I've no idea whether my system is a ring or a star, or where my manifold is, if I've even got one.

Does this sound like a job for a powerflush, or should I try anything else first?

Thanks in advance.

 

[Ytee2]

I didn’t mean to imply you were playing the blame game and I apologise that my post read like that.

I also agree that the plumber should be helping you resolve this with an amicable solution.

It also sounds like the plumber could have prevented your present justified cautiousness by setting expectations and discussing potential problems before starting the works.

I always discuss potential issues. Quite often many of us on these forums touch/fix something and a week later something else breaks.

Old/poorly maintained (even some new) systems don’t like being fiddled with!

The blockage needs to be shifted. A powerflush may/may not achieve this in one sitting.

I’d be tempted to mains flush that section of pipework before committing to a full flush.

• Cap off the header tank feed and vent.
• Attach hose pipe to known unblocked pipe work of problem rad.
• Attach another hose pipe to blocked pipe work.
• Turn on hose pipe and hope it clears blockage.

I’ve also cleared blockage like this with 2mm steel rope.
-Take valve off and feed rope down the pipe.
- If you hot what you think is a blockage (could be an elbow in the pipework), cut the rope with a foot of excess, put the exposed rope end in a drill and slowly twist the rope while feed the rope into pipe to clear it.

If you try the rope idea, remember there’s a systems worth of water behind that blockage, prepared for water. Would be a good idea to cap vent and feed.

Thanks very much for this. I was a bit stressed when I replied so I also apologise 🙂 This gives me some more ideas to try.

I must admit I did toy with the idea of feeding something up it. Wasn't sure what to use for the best result but I will try some of that stuff you mentioned when I get a chance.

I also thought about attaching a siphon tool that I use for removing brake fluid from resevoirs to the end of the pipe and try to draw water down that way. Unlikely to clear a serious blockage I guess but it might be worth a go? I' was gonna try that on Friday when I next get some time.

I'm not sure how to cap off the 'vent' you mention. I can stop the water feed into the tank easily enough, but I'll have to research how to do the vent.

Whatever happens, this is all very interesting and I'm learning a lot, so I really appreciate the help on here.

 

[SimonG]

Power flush wont help. If they've used the 8mm for both rads then that's part of the problem. If you can get under the floor above you may find the pipe kinked somewhere.
Last time I saw this I just repiped it. I'd found both ends if the pipe and put 10 bar through it and nothing moved.

 

[Ytee2]

So, I found some time last night, drained one of the problem rads again, got my (large) syringe onto the end of the return pipe and attempted to both force water up it and pull water down it.

At first, I thought I'd got nowhere. Couldn't seem to force much water up or down and after re-filling the radiator went cold again. However, this morning, the other problem rad (not the one I drained) has starting working again, as if by magic. So now I've got just one rad that's not working.

I'm now wondering... perhaps that means that there are in fact two return pipes, one for each rad, and the blockage I have is actually in my manifold. Is that possible?

 

[Clive Davis]

Thanks for the reply.

Previous to the recent work, one of the rads worked fine, no issues at all. The other worked a bit, it got warm, but never properly hot.

I have not removed the rads completely no. I've bled them for ages though, and they do seem to fill back up fine.

You think it could be a blocked radiator? Worth a try I guess.

I had a similar problem after adding a new radiator. Turned out to be a persistent airlock. Solved by draining last radiator while allowing replenishment until air cleared (listen for cessation of bubbles in draining rad)

 

[Lou]

(Just bumping a few older threads, they will drop off what is new soon)

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