switchmaster 805 DOES control CH, but CH ON CH OFF NOT wired

16 Jul 2007
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United Kingdom
A mop fell against my switchmaster 805 and broke the dial, I bought a digital programmer (tempus 7) to replace it after reading these forums (my system is from 1984).

The old dial based 805 let me turn the CH, "on", "off" or "timer" (same time as HW obviously) - but the there was nothing wired to "CH ON", "CH OFF"! Baffled, I reconnected the 805 and tested it yup worked perfectly, CH on, off timed.

So I connected the Tempus 7, the CH still worked and was controlled by the room stat (switchmaster, 3 wire + earth) but the programmer couldn't turn the CH on or off... how did the old switchmaster 805 manage it WITHOUT "CH ON" "CH OFF" being wired?

With my limited understanding, I think it might be best to try a brand new 805, but would appreciate any other suggestions.


Old Programmer: Switchmaster 805 (for fully pumped only)
New Programmer: Drayton Tempus 7 (has switch for gravity or fully pumped)
Boiler: errm
Room Stat: Switchmaster (3 wire + earth)
Pump: Grunfos
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ahhh, what a dumb-arse...

805... N L 1 2 3 4

1 = CH on
2 = not connected
3 = HW on
4 = not connected

tempus 7... N L 1 2 3 4

1 = HW off
2 = CH off
3 = HW on
4 = CH on

need to wire
CH on - old 1 => new 4
HW on - old 3 => new 3
CH off - not connected
HW off - not connected

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