Im attempting to replace my aging potterton EP2000 controller with a
Horstmann C27 controller. Now the instructions for the C27 show kindly
show a table for converting the wiring for the EP2000 to the C27.
However, having opened up the EP2000, the wiring isnt as straight
forward as I thought. The Ep2000 is connected to a Potterton NettaHeat
conventional cast iron boiler (circa mid-late 80s), both of which are
currently working fine.

Now only having very basic electrician skills, it looks as if this is
possible to wire (from the instructions), but since seeing the wiring
its now clear that I may need assistance from some experienced/wise
bod. ( as the EP2000 instructions werent in the house when I bought
it. )

I've included a couple of pics to help explanation.

The EP2000 to C27 conversion table and the EP2000 basic-wiring sticker
shown here http://81.106.39.40/boiler/back.jpg
The crazy wiring can be seen here http://81.106.39.40/boiler/front.jpg
(ive labelled the wries with letters to aid means of description if
anyone can shed any light !)

Alas Ive no idea to what each of the 4 cables attaches (as I have
precisely zero knowledge of boilers) as I was expecting the wiring to
be a tad simpler.

My current visual observations a
1) The Lives of cables D & B seem to be wired together, but route to
via terminal 5, which isnt listed in the conversion table (it only
goes 1-4). This doesnt seem to be doing anything.
2) terminals 1 & 2 dont currently have any cables attached, (which
according to the conversion table should supply the control signals
for HW OFF and CH OFF ). Ive no idea why - perhaps the controller only
needs to enable leccy flow when the units it is ON.
3) terminal 3 (which should be HW ON according to the C27 conversion
table) has the Earth of cable A connected. Strange ??????

If anyone could advise on how I should wire up the existing 4 cables
to the new C27 controller (to L N E, HW OFF, HW ON, CH OFF, CH ON )
then Id be very appreciative.

Many thanks in advance ....

J.