I've been helping a friend get her canal boat 'ship shape' and the heating
sytem is most odd, there's a log burner with some sort of back boiler and
pipes that run from one end of the boat to the other, via the radiatoirs.
The pump (a small 12v affair) is at the rear in the engine bay and there is
a loop of pipe that goes up and over before going to the inlet of the pump.
This loop seems to alway get air in it, it does have a bleed valve but it's
a pain to keep having to bleed it. Also you have to bleed it with the pump
off otherwise the pump just sucks more air in.
My question is this, can I put an autmatic vent valve onto this loop,
bearing in mind it's on the inlet side of the pump and only 6in away from
it, or will it just result in more air being sucked into the system. If it's
not a problem then it will make life easier in keeping air out of the

An automatic vent has to be on outlet side, ie positive pressure. You
need to find where the air is getting into the system and cure that,
and, or move the pump down-stream to a position where it wont suck air.
Air, or rather oxygen in the system on a continuous basis is a
'very-bad-thing' it'll rot your radiators in no time. There is some
mechanism in the system to allow expansion of the heated water I hope,
is air entering thru that, as when the system cools.
g