At the weekend I drained the central heating and refilled it because I
was getting some simmering sort of kettling noises from the boiler. This
fixed that noise, it's really quiet now, but sometimes when the boiler
is running on lowest speed (Keston Celsius 25, which can vary its pump
speed) I get a repeated banging noise from the pipes (water hammer type
noise) where they pass through the floor upstairs. There is no noise
from the boiler itself. I can hear a slight swishing in the pump as it
runs at low speed and the bangs match up with the swish. I am wondering
if I have introduced an airlock somewhere (as it did not do this
before), and the compressible air is causing some sort of pressure wave.
The pipe run under the floor is not fixed at all (crap Barratt
handiwork), sounds like it is twitching and banging the joists or the
floorboards.

Everything is getting hot as expected, so it's not too serious, any
ideas on what to do? My thoughts are-
a) drain it again (don't really want to do this)
b) try to clear the (possible) airlock somehow
c) clip the pipes down properly
--
Tim Mitchell