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

[Ytee2]

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

 

[moonlight]

Right ok. I'll give that a try, thanks. My wife's gonna love this

Good luck

 

[Ytee2]

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]

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]

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

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]

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

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]

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]

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]

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]

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.