How to drain CH and HW loop?

My first time doing so. The place hasn't had a flush in years. It's a system boiler with indirect invented cylinder. Is it possible to use the mains fill to flush the system out? So far I know to turn everything off and manually open the 3 and 2 port valves. But what valves should I close and where should I drain from?

It's in the garage so the bottom drain points are the lowest. I was thinking to just close off the flow and return by the boiler, and use the magnetic filter drain point while opening up the fill, would that work? Thanks

Bump

I see nobody has answered so I’m basically replying to give it a bump. I expect professional plumbers are having a well deserved rest

My guess would be that you would need to work round each radiator - closing all the rads off bar 1 then work your way around each one. Could be wrong though.

apart from not having done it for years, do you feel the system is dirty? A fully pumped sealed system probably won’t get very dirty if it’s been maintained with inhibiter etc.

Hopefully a pro will be along to give some proper advice.

As above what makes you think system needs flushing?

Notch7 said:

apart from not having done it for years, do you feel the system is dirty? A fully pumped sealed system probably won’t get very dirty if it’s been maintained with inhibiter etc.

Hopefully a pro will be along to give some proper advice.

Click to expand...

Exedon said:

As above what makes you think system needs flushing?

Click to expand...

Thanks, yes that is the problem... No records or knowledge of a flush with new inhibitor since installation 12 years ago. It's my mum's place and she's just not done any maintenance on it. Lots of rad valves are leaky/full of weird crystallised looking rust under caps, and one is cold (I've bleed it fully).

I could just drain it by opening one of the ports on the bottom, but thought using mains pressure to flush everything out would be better. Plan is do a first flush, fill up again and add X400, flush that out after a couple of weeks, change leaky valves, then fill up again with X100.