We have a Glow Worm 18hxi condensing boiler fitted several years back.
During this cold spell, we've had some trouble with the drain for it
freezing up (the boiler is the in the garage and is teed into the waste for
a sink I have in there).
Not a problem in itself - there is a just a section of waste pipe that goes
through the wall to an outside drain which is prone to freezing as the pipe
is shot and leaking a little. Bit of hot water poored on it soon unfreezes
it and I'll repair it properly when I get chance.
However, when I was diagnosing the problem initially, I noticed a large blue
plastic screw cap adjacent to the drain point on the underside of the boiler
which I took to be a means of manually draining it if the pipe became
blocked. Sure enough, on removing it, a cup full of water came out - but
also what I can best describe as a load of grit, a bit like iron filings in
appearance. Any idea what this is and whether there is anything abnormal