I posted last year that my Worcester Heatslave 2+ boiler has worked reliably for more than 25 years. It has a cast iron boiler and a primary circuit water header tank, on a system with conventional steel radiators.
It occurred to me recently that I have had no build up of black oxide in the system. Water taken from radiator valves is crystal clear, and there is no kettling from the boiler itself.
Thinking back to the early '80's, I did suffer from boiler kettling about two years after installation. I had the system drained, and noted substantial black oxide in the radiator water.
My mainteneance engineer recommended a Fernox cleaning product which was a liquid, possibly phosphoric acid, but I cannot now remember the product spec.
Cleaning took 24 hours, running the Fernox fluid round the hot system, followed by neutralisation and thorough flushing.
Although the primary circuit is reasonably watertight, it is certainly not perfect. Water from the header tank very slowly replaces any water lost.
Despite not having used any anti-corrosion fluids in the primary circuit since then, there has been absolutely no subsequent build up of black oxide, which leads me to ask why.
I would welcome comments, but my suggestion is that the Fernox cleaning fluid somehow 'pickled' the ferrous metal, and made it impervious to oxidation from oxygenated primary circuit water.
Whatever the reason, I think this has contributed to the remarkable longevity and reliability of my boiler.
It occurred to me recently that I have had no build up of black oxide in the system. Water taken from radiator valves is crystal clear, and there is no kettling from the boiler itself.
Thinking back to the early '80's, I did suffer from boiler kettling about two years after installation. I had the system drained, and noted substantial black oxide in the radiator water.
My mainteneance engineer recommended a Fernox cleaning product which was a liquid, possibly phosphoric acid, but I cannot now remember the product spec.
Cleaning took 24 hours, running the Fernox fluid round the hot system, followed by neutralisation and thorough flushing.
Although the primary circuit is reasonably watertight, it is certainly not perfect. Water from the header tank very slowly replaces any water lost.
Despite not having used any anti-corrosion fluids in the primary circuit since then, there has been absolutely no subsequent build up of black oxide, which leads me to ask why.
I would welcome comments, but my suggestion is that the Fernox cleaning fluid somehow 'pickled' the ferrous metal, and made it impervious to oxidation from oxygenated primary circuit water.
Whatever the reason, I think this has contributed to the remarkable longevity and reliability of my boiler.
