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!
Turn it up to 65 and see how you get on!
May even need 70 degrees depending on emitters.
Don’t expect to boil a kettle on a tea light!
Should and must have two different meanings.