No TRVs on the system. This morning, I jumped out of bed to investigate. The
boiler itself was making some noise, and I discovered that it stopped and
restarted 3 or 4 times in a row. After it stopped, changing the boiler's
thermostat made no difference whatsoever, so it had probably cut out. My
guess is that there is an air lock in the boiler that causes problems at the
start - after a while, the pump has managed to push enough water into the
boiler for it to work properly... I now have to work out how to get the air
out of the system. There is a valve directly above the boiler, on the "flow"
side - I twisted it this morning, but there was just water coming out. I
will have to check for any other valves...

I would love to know how the air gets to the boiler that causes these
problems - which are only when the system starts up in the morning. Perhaps
there is some problem with the boiler itself??

Alex

PS Where's the FAQ for this group located, please?

You could try turning the pump speed up to max for a couple of hours.
This might help shift any air.