Thermostat / Timer compatibility

[komakino]

Hi,

We currently have a Switchmaster Sm400 timer (the kind that has water or heating AND water, but not just heating) and a Satchwell (now Sunvic) TLX2203 thermostat (analogue). The thermostat has three wires (plus earth): Red, blue and yellow. I'd like to replace this with a new seimans RDD10 (the mains version, not the 10.1 battery one).

My question is this: as the thermostat would be mains powered, would it only get power when the timer is on (i.e. the two hour period when we have the timer set to heat water)? Can this be changed by rewiring the timer? If not, would the battery version solve the problem?

Thanks for any advice you can offer.

Steve

 

[simond]

Fit a battery powered unit with volt free contacts such as Honeywell's CM907, making sure to isolate the neutral into a loose terminal block. Note which colour has been used for the neutral prior to removing the old thermostat.

Your mains powered unit could be made to work by but you would have to bypass the timeswitch and it would be a non standard set up. If you have gravity HW that is not going to work properly.[/b]

 

[komakino]

Thanks for the reply.

Battery does seem to be the easiest option, and there is a battery version of the thermostat I was looking at.

How will I tell which wire is neutral in the existing set up? I'm guessing it's blue (which seems to be looped back on itself) as from what I've seen online, the red seems to be live and the yellow is switched live. Or at least that's what I think.

Also, you suggest the Honeywell therm, but would the siemens RDD10.1 that I liked not do the same job? I just prefer the look of it.

 

[simond]

If you don't know how to work out which one is the neutral, do you really think you should be doing this particular task?

Get a known proven multimeter, they cost under a tenner for a cheapy eg: Maplin, CPC etc.

Test the cables to earth. One will be live when the CH is timed ON, the other will be live when the CH is timed on and the thermostat is turned up. The Neutral will register 0v at all times. And mind your fingers.

Colour coding suggests that the blue is neutral but if you were a heating eng or an electrician you would know that there are no guarantees, anything goes. Never assume anything in electrics, it may bite you.

 

[komakino]

Ah don't worry, I'm not planning on jumping to any conclusions. Multimeter was going to be my next choice if there was no set coding pattern for heating. I need to invest in one anyway so a trip to maplin may be in order.