Hi, does anybody know how to wire a combie, using the combie heating side to
do the heating and a tank of hot water, and the instant (mains water) side
to do just the kitchen tap.
It is a Potterton Performa 28 and using a Siemens heating pack (3 port,
timing clock RWB9, room stat & cylinder stat)
Have got the heating side up and running and doing the water tank, but not
done the mains tap.
Have got the L,N,E coming from the wiring block going to the boiler but they
are only live when the timer tells it to be. I assume there has to be
constant live for the hot tap to be able to fire up at any time.
Any help appreciated
The heating side of your boiler is, in effect, powering a Y-plan system - so
the wiring for that side will need to be more or less like Y-plan in
[The pump may be different and is probably integral with - and controlled
by - the boiler, so you can probably ignore this bit].
As I understand it, combis mormally have a permanent live and switched live
connection. You will need to connect the permanent live to your mains
supply - i.e. from the fused spur or whatever which powers the whole heating
system. The live boiler connection in the Y-plan diagram needs to be
connected to the boiler's switched live terminal.
However, many newer combis require a volt free contact pair which you don't
get with a Y-Plan with 3-way valve but do with S-plan with 2-port zone
If this applies to your boiler then a mains coil relay is required.
All boilers (except for one) I know of either require a connection to the mains
to demand heat or
they require that you connect to terminals together (sometimes a low
voltage pair - hence the term 'volt free') .
I strongly recommend that you opt for S-plan (see main FAQ). This is much
less troublesome, easier to work around when there is a fault, simpler to
wire and possible to extend later on.
I have installed several combis as hybrid systems they work well (why
wouldn't they) used in this manner.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
The problem is - that according to the initial post - he seems to have
already obtained and installed the bits relating to a Y-plan system. I
assume that if the boiler requires volt-free contacts, he'll have to use the
boiler demand from the 3-port valve to drive a relay.
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