I have a Worcester 24i combi-boiler that is about 8 years old.

Lately, I have been getting dirty water from the taps. It looks and smells like the water in the rads, Grey in colour and smells metallic. It clears after a short while.

I have just drained the system and replaced a radiator that was sludged up. I have also injected Fernox cleaner into one of the rads.

I thought the water to the taps came straight from the rising main. Why might it be getting contaminated like this and what can I do to cure it?

James Cook, March 2008

You need to call a Corgi boiler engineer for this one. This model has a hot water calorifer (like a mini cylinder). When the system was flushed, the inner coil has perforatted allowing a cross of central heating to domestic hot water. This is not necessary the flush that caused it, it just may have shown it. Some flushing chemicals are acid based, for speed, and may have enlarged a small hole previously blocked by the same sludge you wanted to remove.
Repair is not cheap and is fiddly so expect at least three hours labour plus parts.
Your boiler is no spring chicken, so a replacement may be in you long term interest. Get at least three quotes!
Finally, check that the inhibitor added is not toxic, but nowadays most are not.
Bad news I know but I hope this helps

Andy Shotton, March 2008