Restarting a CH system after flushing & pump change

[homespark]

Hi - I have been flushing out the radiators in an open vented CH system in a large house (where I live) containing 20 rads, most with TRVs, but not all. There is a single boiler, two MVs, one pump, one DHW cylinder, one bypass valve. All pretty standard. I have replaced the pump with a more powerful one (Grundfos Selectric UPS 15-60 replacing a 15-50) as there has been an issue with rads in the lower floor (of 3 floors) not getting enough heat (the plumbing layout is very quirky - nothing to do with me!).

Before I drained the system and started flushing I made a note of what position the lockshield valves were in, however that information is now lost (!), so I'm effectively starting from scratch and wonder what the best method is to get the system going again, balancing the rads, etc.

Is it best to start off with all or most of the radiators fully closed, opening them one at a time, purging the air, then balancing the valves before proceeding to the next one, or should they all be fully open to start with and then closed down at the lockshields until they are balanced?

By the way, the bypass valve is and was closed as there are several rads without TRVs.

Any help much appreciated

 

[bengasman]

you You may have taken the muck out of your radiators but the pipes will still be clogged up. If there was a lot of black goo coming out of the rads when you tipped them, it needs a flush. There is only one way to balance the system after that using an adequate thermometer to achieve the required differential over each radiator. The relative position of the lockshield before the cleaning is irrelevant.