Got a condensing boiler (not a combi-boiler) in the kitchen, hot water tank upstairs in the airing cupboard, pump underneath it, and two cold feeder tanks in the roofspace. Standard stuff. Modern-ish house (late 80s).

Occasionally – and more notably when the boiler’s been ‘on’ for a while – there will be the most *colossal* banging noises which travel through the house. Half-a-dozen very loud bangs or clangs, like someone’s hitting some of the pipes with a hammer. Scared the bejeezus out of me the first time it did it. Still makes me jump occasionally.

WTF??

Air in the pipes

Ah. And how does one get said air out of aforementioned pipes, pray?

Try holding your hand firmly up against the outlet of the bath tap and turn the hot tap on (blocking the flow).
Count to thirty and release.
Let the water flow.
Shortly it should start spitting air out.
Keep it flowing for a couple of minutes or until the water flows with no spitting.

Its either ghosts or you have goonies under the house.

I once lived in a house that did this at 6.00 am when the boiler came on; not every morning though, just the mornings when I was well asleep.

If the trick above doesn’t work, try messing with the manual lever on your motorised valve. You will either have one on the CH and one on the HW circuit or one on a Y near the boiler. The most popular is made by Honeywell and after a year or so the rubber ball that moves around inside to close off the galleries gets worn and begins to bang rather than move smoothly. I’m on my second now and planning on having a barney with Honeywell about it.