cold rads

[godfrey1971]

hi all
just inherited a job to finish off new extension on my sisters home, the builder has built a 2 storey extension resited a new combi boiler in the utility room he plumbed in rads upstairs and did first fix down stairs Ihave just drained down system and fitted three new rads, refilled system but cannot get the three original radiators downstairs to get even warm, all new rads and all upstairs get hot ,I've repeatedly bled all rads but dont seem to get any more air out ,all the new pipe work is 15 mm, but original house is 10 mm , I'm thinking maybe an air lock in small bore pipe somewhere, did'nt seem to make any difference when I closed all the other rads, the boiler seem to run only for a few minutes, any suggestions
would be most welcome the house is more than 20 years old
thanks

 

[rob jefkins]

could be an air lock. Shut down the rad valves upstairs leaving the ones downstairs open. After a while try bleeding rads again then open up valves upstairs.

 

[secret squirrel]

What is the length of run from the 10mm pipe to the first 15mm rad?

Could it be that the hot water just isn't getting to the rad?

Had this problem on a micro bore system..... new conservatory, builder had plumbed into the micro bore system and the run was considerable, water eventually reached the rad when it was cold.

Don't think I've made this point clearly but hopefully you can follow it or someone else can explain it more clearly.

 

[godfrey1971]

It seems that where the boiler is sited I think it feeds the new 15 mm pipe first in the new extension then feeds the old radiators in the 10 mm piping maybe there is a build up of sludge in the old pipes think I will need to power flush .