I'm preparing to add a room stat to an existing gas central heating system
and need some help with the installation.
The current system consists of
o Boiler: Ideal Elan 2, conventional fan assist gas boiler
o All radiators have TRV's
o Timer is a Horstmann 527 (electronic 7 day, 3events/day, for independent
heating and water control)
o Based upon the FAQ, I believe the system is a Type C or S-plan
o There a two motorised valves
I've taken a couple of photos of the controls to help (which are located
with the hot water tank - a bit unusual, oh well)
showing the timer
with all the other controls,
including a wire box with its cover off.
I'm planning on adding the Danfoss TP7000-RF + RX1 7 day wireless
programmable room thermostat.
The main unknown is how to wire the unit into the existing system. Logically
it appears straightforward i.e. simple wire AC power to the RX1 and then the
boiler off/on/com wires in series with the timer and that's it.
So to the questions
1. Any opinions, good or bad on the Danfoss TP7000-RF + RX1? I was thinking
of buying from http://www.rkm-heating-controls.co.uk/danfoss.htm , any other
places worth a try?
2. What is the correct way of wiring the receiver to the mains.
Do I simply add the live and neutral terminals in the existing wiring box
in the picture above (rest.jpg)?
3. I have no installation manuals for the boiler or existing timer unit so I
don't know which three wires are on/off/con for the heating.
What's the best way of deducing this information (I've got a Maplins
multimeter to hand)?
BTW - I've had the timer unit off the wall and it has the following
legend for each terminal on its back
Off C ON OFF C ON L N
4. Once I know which wires are on/off/c for the heating, how do I correctly
wire the unit in series with the timer?
Many thanks in advance
Basically, there are four wires going to the zone valve. (Actually there may
be an additional earth wire, as they seem to be metal cased). Amongst them
should be a brown/blue pair. These control the motor. The blue will be
connected to neutral. The brown will be the call for heat from the
To wire in the thermostat, you need to break this brown wire at a convenient
location, preferably at the junction box. Trace the cable back from the zone
valve until you get to the junction box. The two ends of these then form the
switched lines for the programmable thermostat. The receiver may also need a
permanent live and neutral, which you should be able to find in the junction
You do not need to change the wiring of the boiler itself. This is turned on
by switches in the zone valves when the valve detects that it is open. The
correct way to wire a room thermostat is to control the valve and not worry
about the boiler.
From the photos, assuming that the motorised valve in the foreground
is for the CH, this is an S-plan system.
They appear to be Honeywell valves as well.
The wiring should be as
You may find that the boiler has a permanent and a switched live, in
which case the pump may be wired to a separate live output from the
boiler for over-run purposes.
You need to figure out which you have, although it doesn't make a huge
difference to implementing this solution.
I assume that you'll leave the existing programmer in place to time
the hot water.? You could replace the whole caboodle with the
wireless cylinder thermostat and an RX-2 receiver but there doesn't
seem much point.
If so, all you need to do is to disconnect the timed live from the
existing controller from the brown motor wire of the CH motorized
valve. Connect the receiver switch common contact to a permanent
live and the make contact to the MV brown wire. Connect the receiver
electronics terminals to a permanent live and neutral.
No,, look at the S plan wiring diagram. The boiler should be fired
up by the use of the auxilliary microswitches on the motorised valves.
You shouldn't need to touch this part. The new receiver should
provide a timed and temperature controlled live to the CH MV and that
This is a new product. The existing one has been the TP5000-RF and
Make sure you are buying what you think you are buying,
There are wiring diagrams on www.danfoss-randall.co.uk
A bit more - see above and refer to the Danfoss Randall web site.
Trace back from the motorised valve leads and the diagram. It should
become obvious from the cable colours.
You don't. Simply take the CH part of the existing timer out of
circuit and use the timing function of the new controller. It can do
more things like optimised start and night setback anyway.Retain the
old one to time the heating unless you fancy replacing it with the
If you have a conventional S-Plan system (and you appear to have the right
ingredients for this) it works as follows:
The motor in the HW zone valve is controlled by the HW demand from the
programmer and the cylinder stat, wired in series.
The motor in the CH zone valve is controlled by the CH demand from the
programmer and the room stat (if any), wired in series.
Additional "volt-free" contacts within each zone valve, which close when the
valve is open, are connected in parallel with each other between a live feed
and the boiler/pump demands. Thus the boiler and pump operate whenever
either or both zones valves are open.
In your case, there is no room stat at present, so the CH demand from the
programmer goes straight to the zone valve motor. You need to intercept this
wire, and connect the switching end of your room stat in series with it. You
should be able to do this all within the airing cupboard - provided this
will give you adequate radio contact with the programmable/display end of
You should be able to trace the cables ok with your meter. In the programmer
there are 2 changeover switches - each with C, On and Off. There is very
likely a mains feed to each of the C terminals. The CH On terminal will
become live when the CH is turned on, and likewise the HW. Neither Off
terminal will be connected.
Incidentally, you should really replace the TRV on the rad in the room where
the roon stat will be with a conventional valve - otherwise you'll have two
independent control mechanisms which will fight with each other. For
example, if the TRV cuts that radiator before the room is up to the
temperature set on the stat, the stat will never operate and the system will
just run contnuously, as at present.
It would be better to take the timing function for the CH from the
existing programmer out of the occasion completely because this type
of room controller has timing functions with setback, optimisation
etc. wihich will do a better job. I suppose there's nothing wrong
with leaving it in place but setting the existing controller to 24hr
mode to provide a permanent live.......
Taking it from the programmer (and, indeed, leaving CH on constant) has the
advantage that the CH can easily be turned off from a central point
(particularly if he subsequently adds more zones) without affecting the HW
and without needing to change any settings on the progammable stat.
If he *does* provide the programmable stat with a permanent live, it's
important that he takes it from a point *after* the isolation switch for the
Yes of course. I was using the expression "permanent live" in the
normally accepted heating context where everything should be isolated
by one switch if at all possible.
To email, substitute .nospam with .gl
Thanks to everyone for the quick replied, really helpful.
Re: Make sure you are buying what you think you are buying,
Andy - Thanks for picking up on this, I re-checked the Danfoss product range
and the TP7000 is overkill for my requirements of adding a room stat
to a system which already has a timer. The RT52-RF should do the job and is
much cheaper too. Basically, leave the existing timer to control CH on/off
(day/time/if at all) and add a thermostat to control temperature when the
system is on, much the same as the function of the cylinder stat for the HW.
Clearly Andy's other comments of taking the existing timer out of the system
would be correct if I were to use the TP7000 (a timer and stat) - no point
in having two timers for the CH.
Now to the wiring.
With the info from here plus the Honeywell wiring diagrams (which I found
much clearer than the Danfoss ones) wiring the stat receiver in will
a) Connect the stat receiver electronics live and neutral terminals to the
existing permanent A/C supply terminals used for the valves and existing
b) Logically, "cut" the brown wire currently connected to the CH zone
valve (I say logically as it must already have a break in it to get the
existing timer into the circuit) then
c) Connect the end leading to the motorised valve to the ON terminal in
the stat receiver
d) Connect the end that was leading away from the zone valve the COM
terminal in the stat receiver
Once wired, the stat receiver will have four wires going to it - mains live
and neutral plus two brown wires.
Have I got the wiring correct now?
One other question I forgot to ask regarding wireless control. Given there
wireless devices in the house (network, DECT, Bluetooth) can someone confirm
that adding a wireless stat isn't going to interfere? I couldn't find any
details from Danfoss etc.
That's fine as long as you're happy with the simple timing options and
don't care about the optimised operation that you can get from the
It's probably better to reverse c) and d) in case you ever wanted to
control something that should get power when the heating is above the
set point temperature. I can't think of an example, and it won't
cause a problem as you have described, just neatness really.
I think so.
The Danfoss equipment operates on 433MHz which is typical of this type
of equipment. It will almost certainly have some form of
interference protection which will prevent erroneous switching. It
won't protect against any deliberate gross jamming of the frequency,
but that is not likely.
WiFi operates on 2.4GHz as does Bluetooth. DECT is at around
Actually, it is very much worth having the timing functions in the
thermostat. This is because the programmable thermostat can do useful
things like dropping the temperature rather than just cutting the heating
totally, frost protection and set back.
Mine has a nighttime and daytime temperature and will estimate how long
it takes to warm the house up depending on the current temperature and
turn on at just the right time. This isn't possible with a separate
programmer, where you have to set it back manually by an hour or two and
probably overestimate the time required to warm up sometimes and
underestimate at others.
Also, it is extremely useful having the timing control nearby (I've got
them in the master bedroom and lounge) rather than in a dark manky
cupboard under the sink.
Mine is a Sunvic one (actually two). I can't remember the model, although I
bought them from B&Q for 30 quid.
They work slightly unusually in that rather than having 2 or 3 on/off
periods a day, you set up day types that you assign to each day. Each day
type is set up with hourly granularity where each hour can be "on" or "off".
The "on" and "off" temperatures are set elsewhere. The best thing about this
method is that the day's profile is always shown on the screen as a series
of 24 dots, so you can tell at a glance if you are about to be plunged into
In any case, most programmable room thermostats have set back and the other
features I mentioned.
What's wrong with having the controller near the tank? I specifically asked
that the timer be co-located with my H/W tank. Admittedly the airing cupboard
with tank and controller are in my downstairs lavatory.
I've not seen the timer in an airing cupboard before, especially an upstairs
One other point is that the upper operating temp of some controls is 40C,
chance it could reach that temp in the enclosed space when then pipes are
running around 70-80C.
Having said all that I've had no problems with the timer in my system.
You can install it wherever you like. My old house had it in the airing
cupboard. The new one had it on the kitchen wall, although I've moved it to
the understairs cupboard, where the consumer unit and many of the zone
valves are. The heat bank and boiler are (will be) in the loft.
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