"Wanderer" wrote in message
...
On Tue, 22 Jul 2003 13:42:09 +0100, Christian McArdle wrote:

snip

Another alternative is to stick a 3kW immersion heater in some suitable
chamber and pump the water through. An immersion is dirt cheap and I'm
sure
you can find some suitable "cylinder" to immerse it in, provided
suitable
safety precautions are taken. (I might consider a vent pipe straight up
to a
metre or two above the pool level from the top of the chamber, for
example).

Hmm, pool heaters are essentially un-vented flow boilers (albeit with an
excess pressure safety valve). It's the passage of water through the
boiler
that keeps it operating safely. They *must* be wired so that they only
work
when the filter pump is on. I think you'd need to get some sort of
cylinder
that was little bigger than the bore of the (usual) inch and half diameter
pipework.

How about a combination:

PUMP
____
=========/ \==================================

=========\____/= ==================== =========
||
|| ||________||
| _________|
|| ___||___
|| | |
|| | |
|| | |
|| | |
|| | |
|| | ~~~~|
||______| |
| _______________|


Flow restrictor/isolator (valve)

~~~~ Immersion heater
with thermostat
in vented tank


The thermostat would prevent boiling in the normal way if
the pump failed.

The first flow restrictor could be set so the pressure in the tank during
pump operation was not sufficient to blow water out the vent.

The whole heater section is an "add-on" that can be isolated for repair.

--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)