Boiler Control using MAX hardware

So now I’ve got a number of MAX radiator valves around the house which are linked up to FHEM which is providing some monitoring and control. I’ll go into some more detail on the software side in another post. However, I realised that the amount of value that you get out of this system is pretty limited unless you can find a way of controlling the boiler.

Most of the other systems like this which I have seen do have some form of relay or control (sometimes called a ‘boiler interlock’) so that the individual zones can ‘call for hear’ and similarly the boiler shuts off automatically when heat isn’t required. Without this all you have is some fancy valves but the boiler control is still only by a basic thermostat or timer.

Unfortunately, there is nothing available in the MAX range which does this. This seems to me a major omission as all the others do (FHT, HomeMatic, evoHome etc). I had a bit of a problem, as I needed to be able to address the relay via FHEM on the computer, but the CUL device can only be used in one mode at a time. So if I wanted to use a relay from a different system (eg HomeMatic) I would need to have a second device to do so which will obviously cost a lot more.

I thought about this a lot because I really didn’t want to spend a lot of money on this and I didn’t want to overcomplicate matters. After a bit of digging around I found this:


This is one of the MAX products (details here ) although it is a little obscure. To be honest I’m struggling to work out when exactly anyone would use. It is basically a switched mains plug just like many which you find in home automation systems. However it is designed to work as part of a MAX system. So far as I can make out from the documentation it is supposed to be used with electric heaters or pumps that plug in to the wall. I’ve never seen anything quite like that… but maybe they have them in Germany.

The good news is that because it is a MAX device I can address it from FHEM without using any additional devices. However it wasn’t immediately obvious how I would use it to switch my boiler directly, which used a 240V switched circuit which normally goes to the thermostat. I had a few ideas, including stripping the whole unit down and somehow wiring the relay in directly and whilst I did get the board out to have a look there was no obvious way of doing this. The fact that it uses a European plug (aka Schuko) is another obstacle.

So I considered a few options, including buying a Schuko socket to plug it into. However as above I was trying to keep the costs down and keep it simple. My boiler already has main supply to the existing thermostat receiver so it’s fairly easy to wire things in. So what I have ended up with is starting with a UK socket, then an adaptor, then the switch unit, and then an older shaver plug with a flying lead.

The other end of the lead goes to a huge and rather OTT mains relay which I got for a few pounds from ebay:


Luckily it fits quite nicely into a blanked off single switch box, with the wires poked in through a hole in the bottom and fixed to the screw terminals on the base. The output from the flying lead on the switch goes to energise the coil, and the output contacts are wired to the thermostat input. So I’m using a mains relay to switch a relay to switch the boiler on! It’s a bit convoluted… but it works!

The end result in the boiler cupboard looks like this:


So a little inelegant perhaps… but I’m happy with the result.

In FHEM it can be configured as a MAX thermostat (so it appears exactly the same as one of the radiators) but it can be switched on and off by sending an ‘on’ or ‘off’ command to it.

I’ll cover the FHEM configuration in a bit more detail in the next post


Intelligent Heating Control – First Steps

As promised I’m now turning my attention to a different project. For a long time I have wanted to handle control of my heating system much more intelligently than just relying on a single thermostat. My house is a fairly large Victorian terrace spread over three floors, and the rooms are large with high ceilings. At the moment the thermostat is in the hall, and this is supposed to take account of the heat in all the rooms of the whole house. It seems a very blunt instrument and I’m sure I’m wasting a lot of heat.

This sort of thing is topical and there have been products such as the much-vaunted Nest thermostat. However, I’m really unimpressed with this – because no matter how fancy it is it only samples heat from one place. If you live in a small flat then that’s fine – but it doesn’t help my situation.

As well as having more sampling points, you should also have more control over how the heat is distributed. Nest etc only control whether the boiler / heat source is on or off – not where the heat is going. My house uses standard gas-fired heating with radiators and thermostatic radiator valves (TRVs) but I’ve never been very satisfied with these. Also of course they don’t provide any control of the boiler.

It seems I’m not alone in this – there are a small number of products out there which address this issue, and the most recent and most consumer friendly is the Honeywell EvoHome system.


This does look very interesting but I’m not pursuing it for various reasons (mostly because I don’t want to have to start again with a new system). There does seem to be a lot of discussion about it in the AutomatedHome forum

The basic idea is that you have one or more replacement TRVs which are motorised and have a temperature sensor. The valves report back their temperature to a central control point, which is then able to control the boiler to switch on as the need to heat each radiator arises. This feedback is the big plus over a normal TRV (which really only regulate maximum heat) as it allows them to regulate minimum heat too. When heat is called for, only the radiators which need it will be on and so the heat is much more efficiently transferred to where it is needed.

I’ve been looking at these systems for quite a few years now. When I first started about 5 years ago, the only thing out there was the FHT range. This is based on the FS20 protocol, which seems to be very well-established in Europe and particularly Germany. There is an enormous range of FS20 kit available, far more than any equivalent system used in the UK. However, it seems little known about here. The FHT system involved a separate valve motor (FHT 8V) and room thermostat. The motor adjusted the valve depending on the temperature, and a separate boiler interlock (FHT 8W) which listened to the settings of the valve motors, and when they reached a certain level it triggered the boiler. The FHT 8W is a remarkably overengineered piece of kit – I bought one at great expense (about £80) but I don’t think many other people in the UK did.


I had this system (two or three thermostats and the boiler switch) in my old house which was much smaller, and it did seem to work quite well. I discussed this quite a bit at the time on various forums and blogs (see discussion with Jack Kelly who goes into the whole subject in some detail). However, when I moved house the FHT kit remained very expensive and I rather lost interest in the whole idea as other more pressing work took over.

The other thing which I did get from my first attempt was computer control of the system. I was not satisfied with just the kit, I wanted to monitor and control it much more closely. Once again, I found that the Germans were very far ahead of us. Through reading various forums (thank goodness for Google Translate) I learned about FHEM. This is very mature and well established home automation control system. I’ve been following home automation for years (and I have a developing Z-Wave system for lights etc which I’ll talk about some other time) and am aware of various software systems.

However FHEM stands out for a number of reasons – it is unashamedly geeky and flexible (hence it suits me well), it is extremely well supported (if you speak German) and has support for the widest number of different systems that I’ve ever seen. To get it to talk to the FS20 system I needed a CUL1101 device. At the time I got mine the only place you could get them was from busware which is another German company. It was rather expensive (about 50 Euros although they are more now) but gave me what I needed to interface FHT with FHEM and read out the data to plot some graphs. However I never got much beyond this and I was aware I hadn’t really made the most of it.

This is pretty much where I got up to before I picked it up again recently – which I’ll cover in the next post.


ComGSM update – success at last!

I have now succeeded in getting my ComGSM substitute to work. I’m grateful for the suggestions and advice I’ve received.

I have come to the conclusion that the TC35 board I originally bought just won’t work in this situation. I can’t really come up with a good reason for why, but as described in previous posts it doesn’t function correctly when connected to the panel. I think it does now work though so maybe I’ll find a use for it in another project.

I have now connected up the SIM800L module along with the voltage regulator and it worked perfectly first time. It is clear that this is a much more up-to-date module, being a fraction of the size of the TC35 one. It also uses a micro-SIM rather than a full size one which is handy. It is possible to insert the SIM the wrong way round though, which caused me some consternation until I realised it.

After some rough testing I’ve now permanently installed the two boards inside the metal casing, with the antenna fixed to the outside. I’m very pleased with the end result which is very ‘stealthy’ and actually to my mind is much neater than the official Texecom unit.



Here is the whole cabinet, with the SIM800 module next to the main board on the right and the regular board hidden behind the bundle of sensor cables (note the incredibly bright green LED!). The antenna is on the top with the black cable just about visible.

These show the detail of the antenna, regulator and SIM800 board.

I then configured the panel with COM1 as the GSM module, and much to my relief after restarting the panel saw this in the ‘Online Status and Control’ window in Wintex:


The bottom right shows that GSM signal strength and bit error rate as both being normal. The ‘online’ doesn’t mean anything as it says this even when nothing is connected.

As usual there is a huge amount of configuration you can do, and this is contained in the manual for the real GSM unit. It is wise to tone down the notifications, since as default you will get an SMS message every time the panel is armed or disarmed and it seems to store a backlog. When I first got it working I got loads and loads of text messages for the last week or so.

I need to properly test that it will send me a text if the alarm goes off but I’m sure it will work. You can also send various commands using SMS, but the issue I have with this is that you need to prefix them all with your code which means that if anyone got your phone they could easily read it out. However this is in reality rather unlikely.

I use giffgaff for the mobile phone service, mostly because I use them for all the other phones in our house as well. I’ve found them to be very good and I’d definitely recommend them.

So I am happy that finally this project is completed and at very little cost. I’ve developed the capability of the alarm and it does now stand alone in the event of a power failure etc and can get to the outside world without relying on the Internet.

So… what’s next? Well, I am getting interested again in intelligent heating control systems and have recently ordered some new bits, so will post about this when I have some time. In the mean time, if this interests you I’d thoroughly recommend Andy Carter’s blog on the subject which I’ve found a mine of useful information.

Premier Elite v3.00 Firmware

Visiting the Texecom website today I’ve made the exciting discovery that the firmware for the Premier Elite panels has had a major upgrade from v2.11 (which is what mine shipped with) to v3.00

Now I’m a firmware junkie – doesn’t really matter to me whether I want or need the new features, but I just want to be on the latest version. So whether it’s TVs, microwave ovens, dishwashers or guitar amps I’m always interested in getting the newest software release.

Texecom provide a very useful summary of the changes here

From a initial look through, much of it is expansion and improvements rather than major new features but one thing particularly caught my eye. Since I’ve been playing with these panels I’ve thought that I’d really like 3 COM ports – one for the GSM interface (when I finally get it working), one for integration with the Vera smart home controller (more of this in another post) and one for a permanent COMIP connection. This is apparently available on the most expensive panel but I didn’t think of that when I bought it.

Anyway it seems this new firmware allows COM3 to be accessed via the existing communication port – confirming my suspicion all along that it was just a COM port in disguise. It will require a breakout board which no doubt one will have to buy from Texecom:


Although judging by this picture it will simply connect out a few pins – so maybe it will be possible to identify which pin is which and connect directly to it and I am worried that this new board will be expensive.

The other problem is that one cannot simply flash the new firmware using a COMIP or USB-COM which is a bit of a pain. The firmware is held in flash ROM, but they seem to have left the programming chip off the main board and so one has to buy the ‘CDH-001 Firmware Flasher’ which is going to be about £30 from the usual sources

Premier Elite Flasher Interface

Looking at this picture really makes me unwilling to pay £30 for the privilege – it is clearly just a MAX662A flash programming chip plus a couple of capacitors, a switch and a button which can’t be worth more than a few quid. However without knowing the pinout of the programming port and without being able to study one of these I’m a bit stuck. I’d love to be able to DIY one of these… but I suppose I may have to grit my teeth and stump up if I want to get the upgrade. I suppose if you are an installer you make your money back after the first job but for me the ‘cost per use’ is very high. If only they showed a photo of the underside!

To make matters worse the above adapter still needs the USB-COM to work, but at least I already have one of those.

If I do get one I’ll analyse it and post the results… or I could just stay at v2.11 but I’m not sure I can tolerate that now I know I’m out of date.

In other news I’ve now got all the bits from China so will try again with my ComGSM DIY effort and will post the results.

Good news & bad news

With thanks to a commenter on a previous article, I’ve had a close look at the ribbon cable which connects the TC35 module to the UART board. After a bit of fiddling with the (tiny) clamps which hold the cables in I was able to release the cable. At least one of the contacts appeared damaged, so I trimmed the end off each cable with a sharp pair of scissors and reconnected it. This picture shows the two boards disconnected with the ribbon cable in the middle. Normally the two boards are on top of each other and I imagine that the ribbon is under a bit of strain.



Initially there was no change – but then I tried reversing the TX & RX pins (ie connected TXD – TXD rather than TXD – RXD) and all of a sudden- success! I can now control the module through AT commands using my new USB device.


So thinking I had solved the problem, I rewired the cable to the alarm panel (swapping TXD & RXD) and tried it – but once again with no success. I’m not quite sure what I’m doing wrong, or I suppose it might be that there is some other reason (maybe incompatible voltages) why this unit doesn’t work. I did wonder if it was because my SIM has no credit but it should still report signal strength and it does so if I try sending AT+CSQ directly.

So if anyone else out there is struggling with one of these modules – try trimming the ribbon cable and swapping over the TXD & RXD pins.

Meanwhile I have received the new board from China – which is tiny by comparison with the one I have. I know from Andy that this definitely does work, so I’m now waiting for the regulator board to arrive and I’ll give it a go.

Dead end… but not all bad news

Unfortunately it looks like the phone module I bought either doesn’t work at all, or there is some secret to using which I’m not aware of.

I’ve used the USB serial adapter (see below) to have a good probe around the various pins and try as I might I can’t get it to give any kind of response. I’ve tried various baud rates but there is no sign of anything coming back from the device. I’ve tried swapping the TX & RX pins over so that I am connecting TX to TX. This seemed a bit better in that I got an error message coming back from the serial console (UART overrun) but other than that no signs of life.

This is not helped by the lack of documentation. I will try contacting the Chinese seller but given how long I’ve had it (I got it in April) I don’t think I’ll get much back.

However there are two bits of good news:

i) The small USB serial interface and breakout cable is very nice and I’m sure I’ll find it useful in future

ii) I’ve had some very helpful comments from Andy (see older posts) who has bought a different module and got it working. So I’m following suit.

I’ve ordered these from ebay:


The left is a SIM800L GSM module, and the right is a ‘DC Buck’ regulator. The GSM module looks much smaller and nicer than the one I have, and the reason for the regulator is that it needs 5V and I’ll need to step down the Aux power output from the Texecom panel which is 12V.

Andy reports that everything works fine with the panel and these modules, so I’m very pleased to find the concept is proved and I’m looking forward to trying it for myself.

Meanwhile if anyone has any idea about how to configure the TC35 I’d be glad to hear them.