Having done a google, I have come across a technique to wire two pumps into
a gravity system to produce a fully pumped system
as per
http://groups.google.com/groups?hl=e...pex.net&rnum=8
http://groups.google.com/groups?hl=e... ws.pipex.net

I am confused of how I can acheive this with my setup.

I have got a danfoss RX2 that provides the inputs for both heating and room
stats (there is no programmer as the room stat is programable)

The connection box RX2 has a zone (zone 2) output that switched live, there
is then two other outputs that is switched live (zone 1 on) or (zone 1 off)

The boiler has a live imput that fires the boiler and pump. There is then
another input (mains Swl) that is the switched live from the external
gravity hot water circuit.

If the boiler is run as fully pumped, it will need to have pump overrun
selected - this will need to overrun the heating pump only.

As far as I can make out I need to wire the RX2 outputs from that stat to
the pump, and then wire two relays across the pumps (1 per pump) so that
when the stat fires the pump, the relay is activated and the "main L" input
to the boiler fires". As they are connected via relays the boiler input
going live will not fire the other pump.

The problem is the boiler overrun - I cant just wire the hot water pump to
the boiler, and ever time the boiler fires the HW pump would run. How can
pump overrun be implimented?