Dirty water from taps! (Worcester Combi-Boiler)

I have a Worcester 24i combi-boiler. It’s about 8 years old and feeds 4 rads. It’s a sealed system of course, so there are no storage tanks.

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 and will soon drain that off and inject Fernox inhibitor.

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

Thanks guys!

Leaking heat exchanger?

If the boiler uses a shell and tube heat exchanger design, hydronic water (heated in the Shell) is getting into the hot water supply (heated in the tube which is in the Shell).

I am not familiar with your particular boiler, but this is what I would suspect.


If you have an indirect water heater, this could be the source of contamination.

It is particulatly bad if your boiler runs propylene glycol or some other anti-freezing chemical in its lines.

Yes, Glycol will cause kidney failure.