Radiator problems

[imperium]

Moved house. Worcester combi about 4 yrs old working ok. 2 pipe system for central heating. Odd system for rads. Cannot follow sequence but lt feeds one rad then rises to do 2 on 1st floor comes down feeds another rises again feeds two and then down to do another two and up back to boiler I think. Some of walls/floors are solid concrete so think this is why odd directions. However last two rads are not heating very fast tho hot water going down OK and one has been off and flushed and return pipe from them v cool. 1st rad v hot but if all valves on all rads off then system shuts down. If turn down thermostat valves then rad seems to be fed hot thro valve on other end.
Any ideas???
Further info!
ist radiator in system flow in OK but out not returned to boiler

 

[dextrous]

Could be a blockage or an airlock, especially if the pipework is as you suggest. If the boiler is 4 years old, it may not have a bypass installed and relies on one of the rads (usually bathroom or the one nearest the room stat) to be permananently open, so this may need flushing or the valves checked that they're allowing flow to take place.

Finally, the system will need balancing - see the WIKI for advice.

 

[bengasman]

WB combis of recent years don't need external bypass, so not to worry about that one.
Most likely option is the system not being balanced.
Make sure system is at a minimum of 1 - 1.5 bar and all rads are bled.
Close all rads apart from the 2 that don't get warm.
Make sure wheelhead and lockshield valve are open on both problem rads.
Run heating on high; if rads get warm, system needs balancing. If they still don't get warm, it could be blockage, worn pump or wrong piping.

 

[dextrous]

WB combis of recent years don't need external bypass, so not to worry about that one.

My error - had a wb installed in my london home 5 years ago, and they had to fit an external bypass. Assumed this may still be the case 4 years ago.

 

[bengasman]

30 CDI comes in combi and system, system may need a bypass.