"stevet" wrote in message
...
Geoff

Your right, I plan to put a pipe thermostat on the outlet pipe of the log
burner and have this switch the pump on, it'll probably need a relay near
the pump as there's about a 50 foot run to the back of the boat and at 12v
there would probably be a lot of loss unless I used thick cable. I though
of
using a timer delay relay that keeps the pump running for a time after the
stat has gone open to stop the pump from cycling on and off. That should
stop any more air getting in and then once it's all bled it will hopefully
stay that way.

If you are going to do that I would suggest that you have a short vertical
pipe run at the back of the boiler so the hot water in the boiler can rise
and heat the switch. If the pipe is horizontal out of the boiler, the boiler
will probably boil before the heat gets to the switch.
RS use to do switches that switched the way you want that you strapped on
pipes. Also the timer is a very good idea, otherwise the boiler heats up,
the pump starts, pulls cold water from the rads and pump cuts out, water
stops flowing and heats up, pump starts, more cold water , pump stops.
You can get a plug in timed relay that they use for heated car back windows
that would do the job nicely.

What makes you think I've been there.

--
Brian
From Sunny Suffolk