Some cooler radiators

looking_forward

Good morning all,

I have been trying to get to the bottom of this and it is not going as I hoped .....

Background is we have a central heating system with 12 radiators . It uses a regular open vent system with an old stelrad boiler and has the highly regarded (not) 8mm microbore. I have never been happy with the heat coming from the 2 largest rads in the house. A few months ago I drained the system - got  some dirty water out but not really as bad as I was expecting , then I refilled with clean water and 2 litres of Sentinel X400 - I let this run through and didn't notice any massive changes. Here is where it gets strange, few days ago I fully drained the system , removed and flushed through the 2 cooler radiators. 
     So everything is now refitted , bled and balanced , most of the radiators are working very well but of the 2 cooler radiators one is slightly worse than before and one is stone cold ! 
I have tried shutting down all other radiators and just leaving these 2 on - nothing changed.

Unless I get any other tips my plan is to wait a few months then fully drain system and blow through pipework to the 2 offending rads.

I am perplexed how the problem has now got worse after a cleaner and flush !

Any input greatly appreciated.



   

nofoollikeold

1. Did you clean the Feed and Expansion tank before you drained the system? If not, any sludge in the tank may have been washed into the system causing a blockage.  
2. Perhaps try the following on one of the problem radiators:
2a. System off.
2b. Drain the radiator by turning both valves off (note number of 1/8 turns to fully close the lock shield.  Eventually reopen to the same point) and slackening the valve to radiator (not valve to pipes) connection.  Use oven trays, old towels etc to accommodate water.  Cover any carpets etc. as spillage likely to be very dirty.
2c. System on.
2d. Open each valve alternately into a bucket.  If no flow or very weak flow you have a blockage.
2e. If you have a system with manifolds and microbore to the radiators, any blockage is likely to be at the manifold(s).

Bendy_House

L-f, the next time you drain down, fit a magnetic filter on the return pipe to the boiler. Then add your X400...

coffeehound

Have you still got that monster magnet filter rig, B_H?  Perhaps you could rent it out

looking_forward

Thanks for the great advice chaps , will follows all suggestions - in the next few months. Yes , have got manifolds and when I drained them a fair amount of crud came out - so will probably remove rad pipes and flush or air clean thoroughly. .

Bendy_House

Most likely your issue, then.

The sludge needs to be removed, rather than released to churn around the system. The easiest way is to fit a filter. That'll catch the majority.

looking_forward

After I've done the next round of flushing and cleaning I will install a filter  , so I can keep on top of it.
Thanks

plumb1_2

And use a rad hammer

looking_forward

Before I get further into this I have just removed the radiator that is stone cold . Rad has drained fine and doesn't appear blocked in any way. I have partially opened both valves with a suitable receptacle underneath and plenty of water comes out. When I turn the flow valve on with heating running  a decent flow of hot water comes through. As you may gather I am very puzzled ! 
Any comments much appreciated.

macman

Cooler all over, or just cooler at the bottom? The latter means it's sludged up.

Bendy_House

looking_forward said:

Before I get further into this I have just removed the radiator that is stone cold . Rad has drained fine and doesn't appear blocked in any way. I have partially opened both valves with a suitable receptacle underneath and plenty of water comes out. When I turn the flow valve on with heating running  a decent flow of hot water comes through. As you may gather I am very puzzled ! 
Any comments much appreciated.

Rad might not appear blocked, but that's not to say it doesn't have a pyramid of sludge along it's bottom (missus!)

Was ANY of the released water black? Or quite clear?