One for the chemists

[Andrew]

My local heating engineer/plumbing shop has a chart on his wall showing the most and least reliable condensing boilers.

Keston 25 rather the near the bottom I'm afraid.

[Clive George]

There's NOx in there - maybe not nitric, but nitrous.

[Simon Mason]

Also Sulphuric due to sulphur content of 5.5 mg/m3. This includes the 4.9 mg/m3 of sulphur in the odourant (mercaptan) added to gas for safety reasons.

[Andrew Gabriel]

Yes, I know! I've seen similar rankings, and I doubt there are many left as a result.

Mine still looks like new inside due to me servicing/maintaining it very carefully, but they have many common failures which if not caught quickly, will write it off in a short time. I did grab one from another reader of this forum which British Gas had maintained but then condemmed. That was due to leaving the internal bleed valve open, and the resulting leak corroded through the case. However, that was after a string of failures which meant much of the internal parts had been recently replaced, so it gives me some spares stock.

[Chris Hogg]

Yes. I don't think CO2 on its own can give a solution with a pH as low as those seen for condensates.

The oxides of nitrogen are many and various, not all are soluble in water, and of those that are, not all give acidic solutions, but for the ones that do, it all ends up as nitric acid eventually, IIRC.

[Andrew]

I wonder what happened to the 2 that another poster installed in his church ?. Wasn't he the ex BCO or something ?, don't seem to hear from him much these days.

[Vir Campestris]

Since then it's occurred to me that may be a bit of sulphur in there too

- sulphur(ous|ic) acid. I'm surprised there's much NOx though. It isn't that hot a burn.

Andy

[tabbypurr]

About 1950C.

NT

[Chris Hogg]

Agreed, see

Also, NOx content of gas flames rises rapidly above 2800F (1534C)

[Vir Campestris]

I sit corrected. So how come petrol engines don't produce much NOx? Is it the stoichiometric mixture? And aren't boilers supposed to be close to that these days too?

Andy

[Tim+]

Catalytic converters.

Sort of. Cats certainly used to need the combustion mixture to be stochiometric before they would function properly.

Yes, but they don't have cats.

Tim