Why yes, we do have a chimney access door — don't you? It's in the garage. You open this little door about a foot square and you can show your chimney brushes up it a lot more easily than from the fireplace, and the mess all winds up in the garage, not the front room. Although we don't actually use the chimney, we have actually used the chimney access door once when a bird came down and brought a load of gunk with it — the chimney access door has a capture point behind it where most of what falls down the chimney ends up. It's a neat invention.
Here's our chimney access door:
Yes, our plumber managed to run the inflow and outflow pipes right over the top of it. He could have gone up or down by a metre with no problem, but he chose to go exactly there, right across our chimney access door.
You know, I suspect that even if we do have heating and hot water this evening, we may be getting the plumber round again shortly. Chances are, there's going to be something wrong...