RE: Automating a thermostat

["Kenneth Watt" <kennwatt@xxxxxxx>]

Dan,

90% of heating systems seem to be mains switched so I would assume that
yours most likely will be. The easiest way to confirm this is to go back
the boiler and look for the switch, this will probably be a simple time
clock affair analogue or digital it doesn't really matter. If you take
off the cover after isolating it and removing the power, there *should*
be a wiring diagram under there for the switch. From this you should be
able to see what is happening on the system and at what voltages. Some
systems are, em, odd! I have seen 24V DC internally switched, mains
internally and externally switched and I am sure it comes in other
flavours as well so it is best to be sure of what you are looking at
exactly.

If the timer is built into the boiler it gets more complex and you
*will* need the installation manual for that specific appliance.

In my case, the timer was just a simple straight forward mains switch,
one in there for heat and another for hot water, operated by the old bit
wheels with pins in them to set the on/off times and this was switching
mains. One AD10 in a case replaces the HW switch as this is easily
controllable from HV and a mains to 12V DC relay for the heating. The
relay is wired up on the LV side to the TX15B which, basically, does
exactly what the switch/thermostat affair used to do only using X10 to
control it. You could also control the heating using some Dallas stats
and a couple of AD10's I suppose but, personally, this is not
bullet-proof enough for me...it gets damned cold in Scotland from time
to time!

Boy am I going to have fun re-doing all this when I get a combi! ;-)

It is not a two-minute job to do, if you are not sure about working with
mains leccy then I cannot recommend that you attempt it yourself, but it
is *fairly* straightforward if you feel confident enough working with
the mains.

HTH

K.

> -----Original Message-----
> From: Dan Khan (Work) [mailto:dhk@xxxxxxx]
> Sent: 12 January 2002 15:41
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Automating a thermostat
>
> Thanks for the link - does not look like an easy job at all.  Has
anyone
> installed on of these in their house in a retrofit application?
>
> Also, the warning says:"Note: The thermostat contains 3 low
voltage
relays
> that are NOT suitable for switching 240V mains power. If your boiler
> requires a thermostat capable of switching high voltages you will need
to
> add external relays. This is NOT an easy DIY job !"
>
> Is there an easy way to tell if my boiler requires a thermostat that
can
> switch mains power?
>
> -Dan
>