First post - although I have been reading for a while.
I moved into my new house 3 months ago. I have a Honeywell ST1000
programmer which is just like this one (the brand name is different):
I haven't used the central heating/hot water timer until now. I have
just moved the switches onto 'Constant' as and when required. This
Recently I wanted to time the heating / water to come on in the
morning but I've noticed that the clock mechanism doesn't work. Does
this mean it's knackered? The switches work okay, and as I rotate the
dial by hand, the heating / water comes on and off as the dial passes
the pegs. I would have thought that if the unit is connected
correctly, then the clock would be working at all times.
If the controller is bust, I could obviously get the one I've
mentioned above from Screwfix. But I think it would be a good idea to
put a modern digital one in. I don't want one with a built in
thermostat because the controller is in the airing cupboard. Am I
right in thinking they are pretty much universal? My heating system is
(I think) fully pumped, having just two water pipes coming from the
boiler, one pump in the airing cupboard, two automatic valves of some
sort, one three way and one two way, all connected up to a Heatrae
Sadia Megaflow (mains pressure hot water tank).
Sorry to sound like such a novice (I am by the way). Thanks for any
They are relatively simple to replace. However, I don't know if the one you
have uses some sort of standard backplate, or if you are going to need to
wire up the new programmer. Some programmers have "volt free" switch
outputs. Others have outputs hard wired to 230V. You can fit a volt free
programmer to a 230V system, but you might not be able to fit a 230V output
programmer to a system requiring volt free contacts. However, most systems
are quite happy with the 230V signalling.
It is important to not touch the 2 port valve wiring. The 3 way valve is
used to control your system as in many central heating systems. The two port
valve is probably a very important safety device that should the Megaflo
requires to remain safe. Do not modify the controls to this one. It is an
Thank you for your help. Based on what you said I have taken the front
off the controller and found out a bit more about the wiring.
It has a nine terminal backplate. Live, Neutral and Earth make up 3 of
them. No problems there.
The other 6 are split into two groups of 3, labelled "ON", "C" and
"OFF". I have worked out that the first group of 3 terminals is for
the CH and the second for the HW.
The Live wire is daisy chained to the two "C" terminals. I think I am
right in saying therefore that it a 230V signalled system.
After using my multimeter I have worked out that a circuit is
completed between the respective "C" and "ON" terminals whenever the
HW or CH is demanded by the controller. So, it's all making sense. The
two "ON" terminals each get 230V when demanded to by the controller,
for either the HW or the CH.
I haven't yet worked out the "OFF" terminal. The "OFF" terminal for
the CH is not connected to anything. It looks like the "OFF" terminal
for the HW is connected to the tank thermostat is some way. My
assumption at the moment is that if the "OFF" terminal gets 230V then
it overrides the connection between "C" and "ON" and breaks the
circuit. Probably when the water gets up to temperature.
However, if this is the case, I would have thought the "OFF" terminal
for the CH would be connected to the wall thermostat in some way.
Anyway, to cut a long and fairly boring story short, I am fairly
confident that I can wire up a new digital controller once I know
about this "OFF" terminal and can have some reassurance that what I've
written above it correct. So, if any of you can give me the green
light, I'm going to go for it!
You may be right here Christian. The two port valve is situated
between the three port valve and the Megaflow heating coil entrance. I
thought it might be something to do with biasing the boiler output
towards the radiators until they heat up, before sending output
through the HW heating coil.
The 'C' stands for common. When heating or hot water is demanded by the
controller, the 'C' is connected to 'ON'. When it isn't, the 'C' is
connected to 'OFF'. Some methods of wiring three port valves call for some
complicated linkages between the programmer and the tank thermostat. This is
Almost any programmer would work for your system. The differences between
them are basically whether the 'C' terminal is internally connected to live
or not. As this needs to be done anyway on your system (which is the normal
case), this isn't an issue.
Thanks for the advice.
I've ordered a Invensis Drayton Tempus 7 programmer from
InspiredHeating.co.uk. I would have got one from Screwfix (they're
cheaper) but I thought they were all a bit pug-ugly. As I have now
decided to relocate the programmer to the kitchen, I spent quite a lot
of time choosing one I liked the look of!
No doubt I'll be back in touch if I manage to make a complete balls-up
of the job.
OK - the easiest thing to try is replacing the 0.1 uF capacitor on the
back of the timer. If that works, you're back in business, if not, the
motor's prolly gone and your best bet is to buy a new one
To remove the timer, undo the two screws on the underneath of the timer,
thumbs underneath the timer and lift up - they are quite tight
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