What makes you think the heat exchanger is blocked?
Not saying it isn’t but I haven’t been there.
What tests would you do to locate the blockage? If indeed it is a blockage.
Magnetite is iron oxide and usually collects in the neutral system point.
What do you think? X
It collects in the neutral point on the system. It cannot be flushed out.
A half decent engineer will know exactly where to find it.
I’m not one for long posts especially when the match is on!
Happened to me in a posh flat in London.
£10000 of damage.
Insurance coughed up.
Learned a lot that day!
It was squirting at great pressure and I tried to run outside with it! Big mistake!