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Polygon-
I used this the other day as I was getting a really similar slow leak. Just popped in like 200ml into the magnet filter (cleaned it out while I was at it).
Seems to have fixed it - need to add some inhibitor back in at some point this week as I must have lost a while systems worth during another… problem.
seager
could try asking the Vaillant person if it’s worth adding something like Fernox F4 leak-stopping-juice and hoping that solves it?