But if the pipeology is cold to start with how will the pump ever get to
know when to start?


I described a method of doing it in a post a couple of days ago. The pipe
stat needs to have change-over contacts. The one which connects when the
pipe is cold is connected to the boiler's switched live. The one which
connects when the pipe is hot is connected to permanent live. Common is
connected to the pump. So:
* Cold Pipe: the pump runs whenever the boiler receives a heat demand
* Hot Pipe: the pump runs until the pipe cools down

Simple, eh?
--
Cheers,
Set Square

I see, hmm, that's very elegant, I like it.
The pipe stat would have to be very reliable,
any recommendations?
There would be a very tiny (millisecond?) break in the power to the pump as
it changed over (break before make), but I don't suppose it would affect the
pump as it's an inductive load and the back emf would take care of that or
am I talking cobblers here as I dredge the depths of my school boy memories
[50 yrs ago, :-(. ]
Many Thanks
Tom