Having to drag up this old topic again...
Update since a year ago. Had the system powerflushed again by a different engineer. All ok for two weeks then same problems arose - intermittent heat and hot water, filter clogging up, pressure dropping etc.
The engineer swore blind the powerflush worked first time and diagnosed a faulty plate heat exchanger (we'd already had it replaced, along with most other components in the previous year), and changed it again.
All was well for a few months, now once again it is playing up with all the old issues.
The magnetic filter is caked in crap. Where is this coming from? Can the rads really be failing? Can't get the pressure above 1 bar. Help!
Previous advise as before. Rads off and hosepipe. Only real way of getting
the dirt out. The radiators are probably old and rusting badly inside.