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Discuss Two cold radiators, rest fine, balancing doesn't seem to help in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Ytee2

Messages
20
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.
 

moonlight

Plumber
Gas Engineer
Messages
948
Have the radiators always been cold even when valves are fully open? I attended one property that had a kinked pipe in the wall. Have you taken one of the radiators off the wall to check if you have flow through both pipes?
 

Ytee2

Messages
20
Have the radiators always been cold even when valves are fully open? I attended one property that had a kinked pipe in the wall. Have you taken one of the radiators off the wall to check if you have flow through both pipes?
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.
 

Timmy D

Esteemed
Gas Engineer
Subscriber
Messages
528
Sounds like some sort of blockage.

Bear in mind that although one kinda worked before the recent work, this is not the fault of the plumber. It’s your problem and the plumber is there to help. So playing the blame game is a quick way to slow down a fix for this.

I had an issue like this that took multiple days/flushes/delicate balancing to resolve.

Rads off/new valves/flushing of individual runs etc.
 

Ytee2

Messages
20
Sounds like some sort of blockage.

Bear in mind that although one kinda worked before the recent work, this is not the fault of the plumber. It’s your problem and the plumber is there to help. So playing the blame game is a quick way to slow down a fix for this.

I had an issue like this that took multiple days/flushes/delicate balancing to resolve.

Rads off/new valves/flushing of individual runs etc.
Thanks for replying. However, that's a little unfair don't you think? I'm not blaming the plumber and I haven't suggested that I was. What I am doing however, is spending a heck of a lot of my time and effort troubleshooting an issue that was triggered by the recent work, without any help from the plumber, who by the way offered me no help whatsoever other than a very expensive powerflushing quote.

So, the purpose of this question is simply to verify that, based on the symptoms I'm describing, a powerflush is a good use of money or not? I don't think that's playing the blame game, is it?
 
Last edited:

moonlight

Plumber
Gas Engineer
Messages
948
It could be you have an air lock. If you close off the end that gets warm, try venting the radiator with only one valve open. If the other radiator is connected to the same drop close both ends of that. Then try. See if you can pull water down the pipe. Close radiators off again and check. Good luck. If that doesn't work. I would then take the small of the rads off make sure you close both rads though and open the end that is not getting warm slowly. (Not while boiler is running though) might be useful to you if it has been before you will then know if its from the return heat.
 

Ytee2

Messages
20
It could be you have an air lock. If you close off the end that gets warm, try venting the radiator with only one valve open. If the other radiator is connected to the same drop close both ends of that. Then try. See if you can pull water down the pipe. Close radiators off again and check. Good luck. If that doesn't work. I would then take the small of the rads off make sure you close both rads though and open the end that is not getting warm slowly. (Not while boiler is running though) might be useful to you if it has been before you will then know if its from the return heat.
Yes, I am getting return heat in both rads (I didn't know the terminology so thanks for the education :) ).

Earlier today I tried pretty much what you said. I closed off the TRVs in both rads, but left the lock shields open. Then one by one I attached a hose and opened the drain valves. Pretty much nothing came out. As soon as I opened each TRV however, water started draining quickly and the rad got warm. Is that the return heat you're talking about?

Seems to me like that means I've got a blockage in the pipe feeding the rads, but not in the return pipe? Is that a fair assumption?

I've no idea how to go about clearing that. I've added some cleaner to the system but I'm not holding my breath on that. Would a powerflush help do you think?

Also, any idea how I might go about finding my manifold? Is it a case of taking the floor boards up and looking or is there some convention with these things?

Many thanks for the responses.
 

moonlight

Plumber
Gas Engineer
Messages
948
Yes, I am getting return heat in both rads (I didn't know the terminology so thanks for the education :) ).

Earlier today I tried pretty much what you said. I closed off the TRVs in both rads, but left the lock shields open. Then one by one I attached a hose and opened the drain valves. Pretty much nothing came out. As soon as I opened each TRV however, water started draining quickly and the rad got warm. Is that the return heat you're talking about?

Seems to me like that means I've got a blockage in the pipe feeding the rads, but not in the return pipe? Is that a fair assumption?

I've no idea how to go about clearing that. I've added some cleaner to the system but I'm not holding my breath on that. Would a powerflush help do you think?

Also, any idea how I might go about finding my manifold? Is it a case of taking the floor boards up and looking or is there some convention with these things?

Many thanks for the responses.
The flow to the radiators is usually on the trv end. Unfortunately the manifold could be anywhere. Are you in a house or bungalow? If you are in a bungalow there could be a vent in the roof space. Locating the manifold may not help you. You may have to bite the bullet and take a radiator off, this will depend on how confidant you are, I think you said you had tanks in the roof space? Look for a vent first as what I may suggest might not be an easy thing to do unless you have the right equipment.
 

Ytee2

Messages
20
The flow to the radiators is usually on the trv end. Unfortunately the manifold could be anywhere. Are you in a house or bungalow? If you are in a bungalow there could be a vent in the roof space. Locating the manifold may not help you. You may have to bite the bullet and take a radiator off, this will depend on how confidant you are, I think you said you had tanks in the roof space? Look for a vent first as what I may suggest might not be an easy thing to do unless you have the right equipment.
It's a house. It's an open system with a tank in the loft. I can access the tank easily enough. When you say look for a vent, do you mean in the wall?

Interesting that you say the rads are fed from the TRV end. Could it be a blockage in the return pipe then?

I'm happy to take the rads off the wall if needed yes, but, could explain again what I'm looking for? I've re-read your post above but I don't quite get it. I can see that the flow through both the rads is ok (because by fettling with the drain value I can make hot water fill them). I guess what you're saying is that by removing the rads I can fully test that both valves are working correctly?
 

moonlight

Plumber
Gas Engineer
Messages
948
It's a house. It's an open system with a tank in the loft. I can access the tank easily enough. When you say look for a vent, do you mean in the wall?

Interesting that you say the rads are fed from the TRV end. Could it be a blockage in the return pipe then?

I'm happy to take the rads off the wall if needed yes, but, could explain again what I'm looking for? I've re-read your post above but I don't quite get it. I can see that the flow through both the rads is ok (because by fettling with the drain value I can make hot water fill them). I guess what you're saying is that by removing the rads I can fully test that both valves are working correctly?
If the radiators that are not working correctly are on the second floor would be the only time you may find a vent in the roof space. To completely check the pipe you really only need to take one off and pull water through the side that is not heating. Connect a hose to the valve and open. Clean the inside of the radiator while its off. Hose on fill it up and shake. You might be surprised how much rubbish can prevent flow through.
 

Ytee2

Messages
20
If the radiators that are not working correctly are on the second floor would be the only time you may find a vent in the roof space. To completely check the pipe you really only need to take one off and pull water through the side that is not heating. Connect a hose to the valve and open. Clean the inside of the radiator while its off. Hose on fill it up and shake. You might be surprised how much rubbish can prevent flow through.
Right ok. I'll give that a try, thanks. My wife's gonna love this :D
 

Ytee2

Messages
20
Ok, so both rads came off the wall this afternoon and got a thorough flushing. Lots of black water and bits of grit came out, but nothing too serious looking. After re-fitting, both got hot throughout straight away as the water went in. But, once filled, the flow stopped and they've both gone cold again.

But I found something else interesting... with the rads removed i was able to completely remove the lock shield valve... with the pump running, and still no water escaped the pipe. Well, nothing more than a drip.

So, seems pretty obvious that both rads use the same return pipe, and it's blocked. Does that sound right? If so, erm, how do i start trying to unblock it? Is that powerflush time? :)
 

moonlight

Plumber
Gas Engineer
Messages
948
I still would have expected you to have water both sides. If it is a one pipe system it will not work properly with a Trv. Open the valves fully and take the Trv heads off. It still might be a two pipe system with a blockage. All of this is difficult to diagnose without seeing the system. I am learning only from your descriptions of your system.
 

Ytee2

Messages
20
I still would have expected you to have water both sides. If it is a one pipe system it will not work properly with a Trv. Open the valves fully and take the Trv heads off. It still might be a two pipe system with a blockage. All of this is difficult to diagnose without seeing the system. I am learning only from your descriptions of your system.
Yep, I get it. I help people on forums with IT stuff and it's always a nightmare :)

If I'm understanding you right, in a one-pipe system water flows from one rad to the next. So if you shut one off completely, you shut them all off. If that's the right description, then that's definitely not what i have. I can shut off each rad independently and the others continue to get hot. Well, until now anyway :D

One other bit of discovery... if i shut off all the rads except the problem ones and run the heating, there is a loud bang and the boiler cuts out instantly and i have to reset it. Like it's hitting a pressure or temp safety limit.
 

moonlight

Plumber
Gas Engineer
Messages
948
Yep, I get it. I help people on forums with IT stuff and it's always a nightmare :)

If I'm understanding you right, in a one-pipe system water flows from one rad to the next. So if you shut one off completely, you shut them all off. If that's the right description, then that's definitely not what i have. I can shut off each rad independently and the others continue to get hot. Well, until now anyway :D

One other bit of discovery... if i shut off all the rads except the problem ones and run the heating, there is a loud bang and the boiler cuts out instantly and i have to reset it. Like it's hitting a pressure or temp safety limit.
No flow, leave one open near the problem ones.
 

Ytee2

Messages
20
No flow, leave one open near the problem ones.
Then nothing interesting happens. Water goes streaming through the open one but the cold ones don't get hot at all.

At this point I'm probably done with the DIY but I'm still not convinced about powerflushing. If we assume it's a blocked pipe for a moment, could a powerflush potentially fix it, or is that a waste of money? My other option is re-piping, and Mrs Ytee2 will insist on those being hidden so that's going to be a fortune!
 

moonlight

Plumber
Gas Engineer
Messages
948
Then nothing interesting happens. Water goes streaming through the open one but the cold ones don't get hot at all.

At this point I'm probably done with the DIY but I'm still not convinced about powerflushing. If we assume it's a blocked pipe for a moment, could a powerflush potentially fix it, or is that a waste of money? My other option is re-piping, and Mrs Ytee2 will insist on those being hidden so that's going to be a fortune!
You have probably by now exceeded your skill level. If you turn it off quickly does it get anywhere moving in the problem ones? As its only the two you have a problem with, personally I would lift the floor above and trace the pipes. I don't suggest you do that. I might have put a water vac on the non flowing side and tried to pull water down. Might be time to call in a plumber. You have certainly tried some of the things any plumber would have tried. I am a problem solver and would have tried some other options. I wish you all the best, I would be interested to hear the solution.
 

Ytee2

Messages
20
You have probably by now exceeded your skill level. If you turn it off quickly does it get anywhere moving in the problem ones? As its only the two you have a problem with, personally I would lift the floor above and trace the pipes. I don't suggest you do that. I might have put a water vac on the non flowing side and tried to pull water down. Might be time to call in a plumber. You have certainly tried some of the things any plumber would have tried. I am a problem solver and would have tried some other options. I wish you all the best, I would be interested to hear the solution.
Oh I'm very much also a problem solver, hence all this effort so far. But yes, I am beyond my skill and tool level. The funny thing is, I had a plumber here when it started. He wasn't interested. Guess he's not a problem solver :)

A water vac is a good idea. I don't have one but if I can get hold of one I'll try it. I do have a brake bleeding kit though. I could probably fill that with water, tape a hose onto the pipe and blow 20psi up it! Not sure that's a good idea though? :)

I'll also try turning it off quickly but based on what I've seen so far I doubt that's going to change it.

Really appreciate the help and I'll post the solution, whatever it turns out to be!
 

Timmy D

Esteemed
Gas Engineer
Subscriber
Messages
528
Thanks for replying. However, that's a little unfair don't you think? I'm not blaming the plumber and I haven't suggested that I was. What I am doing however, is spending a heck of a lot of my time and effort troubleshooting an issue that was triggered by the recent work, without any help from the plumber, who by the way offered me no help whatsoever other than a very expensive powerflushing quote.

So, the purpose of this question is simply to verify that, based on the symptoms I'm describing, a powerflush is a good use of money or not? I don't think that's playing the blame game, is it?


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.
 
Last edited:

Ytee2

Messages
20
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

Esteemed
Plumber
Messages
20,515
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

Messages
20
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?
 
C

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)
 

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