Partial draining down for Rad Alterations

[dolph]

Had new boiler(normal) fitted 2 years ago system changed from gravity fed to unvented, pressurised via cold water mains. I need to change some rads as follows.
1. Do I release pressure by utilising filling loop and draining down via it to just below top floor level after turning valves of upstairs rads off. Is it then refilled by loop and venting through the new upstairs rad's bleeding valve.
2. I have found that prior to my occupancy an extension was built where the rad therein was connected via downstairs cloakroom rad. This I now find is not on main central heating but on hot water system (vented) along with two bathrooms upstairs. I want to take this off hot water and put it onto central heating (so it can be controlled with rest of house heating) This will still leave the upstairs bathrooms as they are. Do I have to drain down the hot water indirect feed and if so how, again I will only need to drain just below upstairs floor level. If so how do I refill, reprime it.
Tnanks again in anticipation as you solved my problems really well a couple of years ago! Hope I have not put too much info in.

 

[ChrisR]

Basically drain what you need from a drain cock, which you should find on a pipe somewhere, maybe outside.
You refill via the filling loop. You can reduce the loss of water and inhibitor by shutting both rad valves, but remember water will then "hang" in the pipes and may drop out unexpectedly.

 

[dolph]

Thanks Chris this is basically the same as I used to do with the two rubber bungs on my old gravity system then.
Will this cover question 2 also as I have never "broken" into the indirect hot water system that heats the hot water through a coil in the hot water tank? I understand correct me if wrong that boiler puts water through the divert valve when it is called for by either the CH or domestic hot water, therefore it is the same water circulating through both circuits. Again many thanks

 

[ChrisR]

Yes all the same water in the boiler side, so same procedure. The "return" pipes are connected together...

 

[dolph]

Seems like a long time ago since posting but over the last few days I have carried out the operation as initially asked about. The new radiator and cloakroom worked really well off the main central heating system. Unfortunately I have run into another problem, hopefully one that someone with experience will be able to help with. Whilst I was partially drained down I decided to remove my bedroom radiator and as I will be decorating the room in the not toodistant future and putting in a new rad I shortened the 15mm supply pipes and capped them with full bore lever valves (to save draining down when I fit new rad). These two 15mm supply pipes came off 22/15/15 tees with the other 15mm pipes going down into the lounge to feed one of the rads in there. This lounge rad now does not heat up - I cant fathom out why, the 22mm feed pipe to the tee hardly gets warm. The other rad in the lounge fed exactly the same but from under another bedroom, no problem. Also the rad in the hall hardly gets warm but the supply pipe to it is very hot but no heat coming out of the return off the rad. I bled all the upstairs rads and the appropriate ones downstairs. I have completely shut down the supply and return valves on the new leg I created and still nothing. Any ideas gratefully received!!