Replacement CH programmer for Potterton EP2002

4 May 2012
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United Kingdom
The programmer on my CH/HW system has recently stopped working so IM looking for a cheap and easy replacement. My system uses a conventional heat only boiler with a hot water cylinder in the airing cupboard together with radiators fed by a tank in the loft. I have a thermostat on the hot water cylinder and a room thermostat. There is a two way valve to divert heat from the boiler to the cylinder, radiators or both.

The existing programmer is a Potterton EP 2002 which can be programmed for different on off periods over 7 days.

IM looking for a similar programmer and wondered if the Horstman CentaurPlus C27 is suitable and how it would be wired up. Screwfix sell the C27 so I could get one tomorrow.

One issue which is confusing me is that my existing EP2002 has terminals A,B,C,D, N, L, 1, 2, 3, 4, 5 however the Horstman only has N, L, 1, 2, 3, 4.

From what I gather, terminals A to D are simply connectors and can be replaced by terminal blocks. What is confusing me is that my EP2002 has terminals 1 to 5 but the Horstman only has 1 to 4. I have noticed that terminal 2 on my programmer is not connected to anything.

My EP2002 is wired as follows:-
- terminal C - red and brown
- terminal D - yellow and blue
- terminal N - blue x 2 and black
- terminal L - red x 2 (one red wire is linked to terminal 5)
- terminal 1 - blue
- terminal 2 - none
- terminal 3 - red
- terminal 4 - yellow
- terminal 5 - brown (and red from L terminal)

So my question is how all this wiring maps on to a Horstman CentaurPlus C27 and indeed is this the best replacement for a EP2002.

Picture below:-
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