Baffled by cold rad - Not sludge. maybe blockage?

[SE82]

I've read all the FAQ's and im still struggling with two cold rads that are driving me bonkers. I

I've put some Sentinel 800 in my system today to try and see if it gets two downstairs rads working. They stopped working in Spring and i've tried everything that I can think of to try and get them hot (balancing/turning off all rads bar one of the problem ones/new trv/new valves/cleaned gauze in boiler return pipe). I thought a blockage might be the problem

One is currently tepid as I write this which is progress.....

How long should I leave the Sentinel in? Until I can get both working or should I drain and flush after the 20hrs?

Should I wash and clean out the Magna clean during this time or wait until after I flush through the system.

I drained the system today and the water was clear. Tonight I bled one of the problem rads and it was much dirtier.

 

[Johntheo5]

Have you TRVs on the rads, if so remove the head and push the pin in /out, it should move a few mms.
Otherwise suggest shutting say the rad outlet valve, ensure the inlet valve fully open, then open the rad bleed/vent "fully" let the water flow into a bucket until it gets hot (boiler firing), do the same with the outlet open/inlet shut, check for a good flow of water from the bleed valve.

 

[terryplumb]

Chemical cleansers don't really work unless they can circulate ,so solidly blocked pipes don't get any benefit.
X800 is aggressive ,and should be totally flushed out after use.
You should remove cold rad and open each valve ,let it run for a minute or two into a bucket ,if no flow there is a blockage. Keep pressure topped up whilst doing so.

 

[SE82]

Have you TRVs on the rads, if so remove the head and push the pin in /out, it should move a few mms.
Otherwise suggest shutting say the rad outlet valve, ensure the inlet valve fully open, then open the rad bleed/vent "fully" let the water flow into a bucket until it gets hot (boiler firing), do the same with the outlet open/inlet shut, check for a good flow of water from the bleed valve.

Yes, they all have TRV’s except the towel rails.
I’ve removed the heads and checked the pins move by pressing something hard on it. They all work and one of the problem rads is a new valve and trv.

I tried your suggestion earlier this year. It worked whilst I was working on the rad but didn’t work again after. The flow from the bleed valve is ok.

This rad used to be first one to get super hot downstairs if that gives any further clue.

 

[SE82]

I’ve noticed that since I’ve turned the other rads on in the last 30 minutes one of the problem rads is cooling down.

Which makes it sound like a balancing issue but earlier I closed all flow and return valves bar this one and it still didn’t get hot.

 

[SE82]

Chemical cleansers don't really work unless they can circulate ,so solidly blocked pipes don't get any benefit.
X800 is aggressive ,and should be totally flushed out after use.
You should remove cold rad and open each valve ,let it run for a minute or two into a bucket ,if no flow there is a blockage. Keep pressure topped up whilst doing so.

I don’t think it’s solidly blocked as some hot water did get in it earlier after the X800 was added and it is flowing.

I noticed that the return pipe is getting hot but the flow is pretty cold. I don’t think it’s sludge though as i managed to get the rad warm during the test tonight.

 

[terryplumb]

You have a blockage in the pipe that's cold ,maybe not 100% blocked,but there is enough restriction to prevent a decent flow through the rad. What diameter pipework feeds these rads ,microbore I assume ?

 

[Johntheo5]

I’ve noticed that since I’ve turned the other rads on in the last 30 minutes one of the problem rads is cooling down.

Which makes it sound like a balancing issue but earlier I closed all flow and return valves bar this one and it still didn’t get hot.

If you leave the TRV head off does it make any difference?
Have you got a gas system or heat only boiler?

 

[SE82]

You have a blockage in the pipe that's cold ,maybe not 100% blocked,but there is enough restriction to prevent a decent flow through the rad. What diameter pipework feeds these rads ,microbore I assume ?

Most of our downstairs rads are on 10mm copper pipe. We don't have any microbore.

Is there anything else I can do whilst the Sentinel is still in the system? Should I leave it in longer than the 20 hours to circulate for longer?

 

[SE82]

If you leave the TRV head off does it make any difference?
Have you got a gas system or heat only boiler?

Its a gas combi. Baxi Duo-Tec 40. Pump running at full speed. Boiler temp set at 68C but turned it up to full when I put the sentinel in.

I tried taking the TRV's off but no difference.

 

[terryplumb]

10mm copper pipe is microbore. How long has the X800 been in ,with central heating running?
20 hours is the maximum time you would need ,and probably a lot less.

 

[SE82]

10mm copper pipe is microbore. How long has the X800 been in ,with central heating running?
20 hours is the maximum time you would need ,and probably a lot less.

Ah ok I thought microbore was plastic pipe.

It’s been in for nearly 20 hours but was off overnight from 10-7am so it’s been circulating for 13 hours.

 

[terryplumb]

You should remove cold rad and open each valve ,let it run for a minute or two into a bucket ,if no flow there is a blockage. Keep pressure topped up whilst doing so.

Do as I suggested above. 13 hours is fine.

 

[SE82]

Do as I suggested above. 13 hours is fine.

Ok.

Should I do this once I’ve flushed the system from the sentinel?

 

[SE82]

Chemical cleansers don't really work unless they can circulate ,so solidly blocked pipes don't get any benefit.
X800 is aggressive ,and should be totally flushed out after use.
You should remove cold rad and open each valve ,let it run for a minute or two into a bucket ,if no flow there is a blockage. Keep pressure topped up whilst doing so.

Just to ensure that i'm doing as you've suggested. I'm conscious I tried this a few months ago and it didn't really work.

Do you mean physically remove the rad? Or just disconnect the flow and return from the rad (keeping both valves open) and then let it run for a minute or two.