Distinguish sacrificial and powered corrosion protection, assess anode condition and recognise a flame-sensing earth fault.
What a sacrificial anode protects
The magnesium rod inside a CLASSICflo adds corrosion protection to the water storage vessel. It is consumed as it protects, so a rod that was sound at an earlier service can become depleted. It does not soften the water, remove combustion deposits or act as an overheat cut-out.
Inspect its condition as part of the service work, using the current appliance instructions to set the inspection and replacement plan. Water quality affects the rate of consumption.
Inspect the worst section
For the standard 22 mm CLASSICflo magnesium anode, replacement is required if its diameter has fallen to half the original size or less at any point. The limit is therefore 11 mm. Pay attention to the ends as well as the middle.
For example, an otherwise thick rod with a section measuring 9 mm has reached the replacement condition. Taking an average of its diameter would conceal that local loss. Record the worst condition, not just the easiest place to measure.
A rod encrusted with limescale needs cleaning or replacement under these instructions, even if substantial metal remains. Do not confuse a deposit on the surface with the amount of magnesium left underneath, or treat painting and greasing as corrosion protection for the anode.
Softened water changes the inspection decision
Less scale does not mean the anode will last longer. The CLASSICflo guidance warns that softened or phosphate-treated water can consume magnesium anodes faster and calls for more frequent inspection in those conditions. Review the maintenance plan when water treatment changes and use the condition found to guide subsequent checks.
A powered anode is a different arrangement
The optional Correx uses a powered corrosion-protection system. Its controller shows green for normal operation and red for malfunction. Investigate a red indication using the instructions for that system.
Do not interpret the red lamp as ordinary wear of a magnesium rod or as a signal that the water is reheating. Identify which anode arrangement is actually fitted before deciding what maintenance it requires.
Keep the flame-sensing circuit separate
A flame rod is part of combustion supervision, not vessel corrosion protection. CLASSICflo fault 57 identifies a flame-sensing short to ground. The physical checks include damaged lead insulation allowing a conductor to touch metal, or the rod itself touching surrounding metalwork.
Safely isolate before inspection. Use the manufacturer’s remedy for damaged wiring or a bent rod, then complete the required operational checks. A restriction in the pilot tube or cold-water inlet is not an electrical short to earth.