Help I'm trying to replace a Honeywell ST7100 timer

18 Aug 2011
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United Kingdom
Hiya I hope someone can help. I'm trying to replace a Honeywell ST7100 with a Centaurplus C27. The only problem is that on the instructions it says to replace N-N, L-L, 1-7, 2-4, 3-8 and 4-5 but the Honeywell only has wires in 8, 6 and 3??? It has wires in the CH and HW on and also a terminal called Com. I don't understand, please help
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The Conversion instruction is incorrect the ST 7100 did not use a standard back plate (that was the ST6400 on) the 7100 had a L, N, and Two Volt Free changeover contacts one for HW the other for CH the Common terminals were linked to L these links can be discarded
you will need to work out which termninals on the 7100 is Normaly Open and normaly closed so you can reconnect to the corect termianl on the new base plate sorry its a vague but I havn't had to replace a 7100 in 20 years!! ;)
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Old 6 to 1.

Old 4 to 2.

Old 8 to 3.

Old 5 to 4.

Plus L&N which should be obvious.
I've only got wires going into 8, 6 and 3 (HW on HW COM and CH COM)?? :confused:
Are you sure there is no wire to 5 - CH ON? There should be or your heating will not work!

Which make and exact model boiler do you have? The C27 may not be compatible.

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