"Aidan" wrote in message
oups.com...


You might find it simpler to use 2 x 12 V dc centrifugal pumps with
non-return valves on the returns.
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you know what, you might have cracked it,

the eberspacher has one pump already, i can get another one pretty easily, i
just have to check where the flow controll thing is in the heater, i dont
think it's the pump motor, afaik it's just 2 wires, + and - 12 v, powered
whne the heaters operating, and also powered when the heater goes into stand
by mode.... i.e. main power on, but the temp has reached and stayed at or
above 82 degrees for more than 5 minutes,

There is an eberspacher timer unit for this heater, it gives 3 operating
times a day, and what i was thinking....

Have a thermostat straped to the calorifier just like a domestic hot water
tank does, it's just a basic switch after all isnt it.

use the eberspacher digital timer unit, and have it set for 3 x 25 minute
operating times throughout the day, have the power to the heater start up
circuit go through the tank stat (via a relay if needed etc)
so if at one of the 25 mintue cycles the tank stat if on, the eberspacher
fires up and heats the tank of water up, shutting down after it's reached 82
degrees C for 5 minutes as above, or when the time peroiod expires,

If the tank stat is open when a time period is active, nowt happens, the
tank's still hot (apparantly a small calorifier can keep it's heat for 24
hours, and only needs 20 minutes to bring the water upto temp from cold..
that's based on much larger tanks than i'll be using, so i'd get faster heat
up temps)

there'd be 2 pumps as suggested with non return valves etc, and a relay to
select which pump operates, normaly closed contacts allow the 1st pump to
operate when the calorifier wants heating.. i.e. pump selector relay is not
energised.

Then for the heating side, i dont really need times for that, as when it's
cold i'll put it on, there'll be thermostatic rad valves to regulate the
temp in the different areas of the van (living area, bathroom etc)

So when i want heating, i turn a switch on, which is connected through a
room stat, if the van's cold enough according to the room stat, power is
sent down the heater start up wire bypassing the timer (may need to use a
relay to avoid backfeeding the timer, not sure if it'll throw a wobbely and
bring up a fault code.. unauthorized heater usage or something
and it'll also switch the relay on the pumps to power pump 2 when the heater
calls for the water to circulate.

So the eberspacher heats the water up, pump 2 pumps it around the radiators
untill the room stat shuts it off, the water going through the heater is at
82*C for 5 mins, or i turn it off manualy.

I could think of a way to make pump 1 operate at the same time if needed by
the tank stat and timer being on i guess. thus doing the same as a 3 way mid
position valve does, but with 12 volts DC... and a lot more complications.

does the above sound feesable? any input welcome, as i don't know that much
about centeral heating systems.

on boats where these heaters are usually used, they all seem happy to have a
manual valve they select hot water or heating with, but i like things to be
automatic, the stand alone water heater i had was, as was the gas fired
blown air heating system,
i'm just combining 2 units into one, and heating with hot water now, but i
want a better system than i had before, ie. one fuel source, one unit, and
hopefully easier use, tho that may be pushing it.