On 2007-07-10 19:04:02 +0100, The Natural Philosopher said:

Yup. Ive been looking at the manual some more.

It seems that TR2 allows the temperature of the room to be displayed..


So there is more to it than meets the eye..it also says something
about using low resistance low voltage wiring, which suggests that it
is an analogue rather than digital link..


Short of breaking into the boiler and accessing the main motorized
valve directly, its the best hope we have though.


Unless you simply use the zone valves as sort of mega TRV's (which is
still worth it).


Don't worry about the MV's sending mains voltages tho: Sure they need
mains to operate the valves, but the switches are just switches. And do
not have to be used.

However looking at that bloody boiler, one begins to appreciate how
de-skilled it is, and hence how lacking in versatility. Its obviously
designed to be used in a small house with one stat and probably TRV's...


Right. I took a final look at the setup instructions on the blasted
manual, and my guess is that the so called smart TR2 thing, is, as you
say, possibly a smart load of ********.


I must say I'd be tempted to break into the cabling that controls the
internal motorized valve, and bring the 'open for CH' circuits out to a
nice set of sockets meself, and run the MV's all off that..but it
probably voids the warranty.

I think you have two choices.

1/. Get a TR2 thingie, and reverse engineer parts of it, or add to it..

2/. simply use the zone valves as flow switches and forget about
connecting them to the boiler electrically altogether (for now anyway):
Then save up for a decent boiler 'one day' :-) Used with the TR2 room
stat, that should at least allow you to control the temps of
individual zones well, as long as the rads in the aree where TR2 is
sited are balanced right down, so that is the thing that always wants
the heat the most.

I have a similar arrangement to this on my boiler (MAN Micromat).

This one, by default, wants to be in charge of the whole show and does
not require external controls and sensors, although it does come with
an external weather compensation temperature sensor - a semiconductor
analogue thing with two wire connection.

There are two switched live *outputs* which can go off to run external
pumps or motorised valves. Operation of that depends on settings in
the installer menu, hidden from the user. I have it set such that one
operates the CH zone valves and the other that for the HW cylinder.
The boiler then opens them according to heating/HW demand.

On the input side, there is a set of three connections, similar to the
WB arrangement. However, the boiler can be programmed to use them
in different ways. One is with a straight and simple set of volt free
contacts - in that mode, the boiler is turned on and off in the
traditional way.

The second mode uses a three wire connection to a specific room
controller. This device has time and temperature settings for the
heating (not HW), including night set back, optimised start. It
also has a control term to vary the relative influence of it vs. the
external temperature sensor as far as boiler operation is concerned.

The boiler is aware of the settings made on the room controller
including temperatures. Another aspect of this is that if you turn
up the control to increase the room temperature by a small amount - say
half a degree - the boiler modulates up a bit. Turn it three degrees
and it goes to full power.

A scope indicated what appears to be DC and ground on two of the wires
and a digital transmission on the third.

A bit more digging revealed that the controller itself was not made by
MAN but by Landis and Staefa (now part of Siemens Building
Technologies). They make a range of products that go with various
control systems on a standalone and OEM basis. The data sheet
describes the interface as being PPS, others in the range as PPS2 -
both appear to be proprietary interfaces. The transmission is there
the whole time - doesn't disappear out of hours or below the set point
or anything like that.

So coming back to Mike's project, I think you are right, from the
descriptions in the manual, there is probably more about this TR2
controller than a simple on/off or analogue interface. It may
well be using a similar concept to the Siemens controllers or even be
made by them - they have quite a product range. Reverse engineering
of the interface? Maybe, but decoding an unknown bit stream where
even the method of encoding isn't known, is not going to be trivial.

I wonder whether getting one of these TR2s and spoofing its analogue
temperature sensing might not be a better proposition. More than
likely that will be a thermistor or semiconductor sensor. The
manufacturer might even have helpfully marked it on the legend of the
PCB. Once the component is identified, it would be reasonably easy
to replace it with an appropriate set of resistors, diodes etc. and a
relay contact such that the controller is fooled into thinking that the
room temperature is very high or very low and stopping and starting the
boiler accordingly. Since the TR2 has a rotary temperature control,
that may operate a potentiometer inside. If that's the case, then
the job is even easier. Whip out the pot, a couple of resistors and
a relay and that's it.

These controllers cost about £45, which is not bad for a proprietary
thermostat. Dinking with one of these would mean not having to start
pulling about the boiler wiring and invalidating the warranty plus
whatever other unknowns might happen. For example, breaking into one
of the boiler internal wirings to a valve etc. might be detected by the
boiler controller and cause a fault lockout on the boiler.

In the worst case scenario with the TR2, the solution wouldn't work and
£45 would have been spent. It wouldn't affect the boiler.