Heating and Hot Water Control

This is a project we never expected to do. We had decided some time ago that we couldn't justify trying to automate the hot water and central heating in our current home. The main reasons for this were simply that we have a combined system with a boiler that heats both the hot water tank and the central heating. It is controlled by a single wired thermostat in the entrance hall and we have no ability to do any form of zone heating.

We are also looking to move house, so had decided that rather try and automate the current system, we would simply leave it alone. These views on adding automation to our current home were changed when I was asked to investigate the technology at work. After 17 years of use, it also looks like the boiler might need replacing. Having had to investigate Z-wave heating control technology in a lot of detail, I realised that we could actually improve things significantly, without doing a huge amount of work and without spending lots of money. It would also be very good test of our Home Control System (HCS) software, which we plan to use in our next home.

Our Current System

It's probably worth adding a few words on how we use our current central heating system ...

Our current home is fairly well insulated. From about April to November the central heating is usually switched off completely, though we do (manually) turn it on briefly at regular intervals, to avoid pumps seizing up. The central heating is only ever required from the morning to about 9:30pm, at which point it is then switched off to let the house gradually cool down over night. Because the house is well insulated, it also warms up quickly. Using the heating in this manner may seem odd to some people but, it has worked well for us and our energy bills are fairly low for this type and size of house. This is another reason why we haven't really looked at automation.

Over the years, as we have refreshed various rooms and bathrooms we have fitted passive thermostatic radiator valves. These give some limited control on the heat output and distribution of heat throughout our home. All the bathrooms have them fitted, as does the kitchen (which has many other sources of heat in it).

Hot water tank
The boiler heats water in an insulated Flomax tank to around 80°C and this is pressurised by the mains water pressure. There is a small header tank on top of the tank for the central heating system. Hot water from this tank exits via a blender (to reduce the temperature) and goes to the various hot taps. The heating system is a closed circuit with a heat exchanging coil passing through this tank. This means that the hot water is effectively on when the heating is on.

Our current heating controller is a two-channel IMI Range LP241:
IMI Range LP241

This device has number of things about it which we really don't like:

  • You can only set 2 on-off cycles per day.
  • Every day has to have the same timing sequence. You can't do something different at weekends for example.
  • There is no 'boost' or '+1hr' button.
  • The clock has to be manually adjusted twice each year, when the clocks change.
  • There is no battery backup, so the clock needs to be reset in the event of a power failure.

When you see the list of things wrong with it listed like this, you really do wonder why we put up with it for so long (17 years!).

The latest version of this device is now made by Drayton.


The current thermostat
The installed thermostat is a very basic, wired device. It does the job.

This device has number of things about it which we really don't like as well:

  • It can be easily knocked and adjusted by accident.
  • It is located in our entrance hall, so is very badly placed to measure the actual temperature of our house.
  • When the front door is opened, it basically measures the outside temperature.

This device is effectively wired in series with the existing controller, so the controller determines what times the heating is on and this device the switches this signal on and off depending on the temperature set and measured.

Our Home Control System (HCS) is already aware of the temperature in every room in our house and effectively provides the thermostat capability needed to do very advanced heating control.


The current wiring looks like this:

There is a lot of wiring but it is all completely logical and all makes sense. The blue circuit board is to enable the pump to over-run for a short time period and the onboard MC14541B is a basic timer IC. How our current system works is very well described on the Vesternet website.


Our Home Control System (HCS) has software controllers which allow us to set scheduled targets based upon house status and this will automatically handle detected occupancy and presence.

Temperature Control

Our Home Control System (HCS) will also enable the use of any temperature sensor in our home, the use of several sensors, or even an average measurement throughout our whole house. In theory, we no longer need to use the original thermostat and this could simply be by-passed with a wire link.


Our current boiler is an Ideal Classic RS260 15KW wall-mounted boiler. Because of its age, it is now on the 'reserved spares' list, which means it is no longer in production and spare parts can not be obtained easily or are guaranteed to be available.

Design Changes

Without any real form of zone control (passive thermostatic radiator valves don't really count), there is limited scope to set a target temperature for each room and hope to be able to control the room temperature to reach and maintain this target. With a single thermostat measuring temperature at one point in the house, you could also argue that setting this is fairly subjective too. This is borne out in practice, with the thermostat usually being set to around 18°C to maintain a comfortable temperature in the main living areas. The temperature gradient through the house and between the ground floor and upstairs depends on many factors and in particular which doors are open and how often they are opened and closed.

I guess you could summarise this by saying that there is little point in trying to provide very accurate temperature control because we don't have a lot of ability to actually control the temperature throughout our home. In practical terms, the timing of the central heating is a much bigger factor in determining a comfortable living environment. We are going to have temperature gradients and different temperatures in the rooms within this house regardless of how much automation we add.


There are several options when it comes to replacing the controller for our heating and hot water system. All of the networked solutions available seem to involve sending data back to a network service and using a portal to configure them. We are not really happy with this model and would much prefer the data and control remained within our home.

March 2014

We have now had a plumber in to do a full flush of our central heating system. Whilst he was in, we asked about boiler replacement and the possible options:

At first glance, the simplest and easiest option is to simply replace the boiler with a modern equivalent. Our current (17 year old) boiler had an efficiency of around 70-75% (when new). Modern boiler are 90+% efficient and most installers will only fit A-rated boiler now. In addition, we realise we do need to replace the hot water pump in the airing cupboard, as it is unbalanced and quite noisy. We could then simply upgrade the control box at the same time.

The second option is to hugely simplify the system by replacing the boiler and tank with a combi boiler in the airing cupboard. This requires a gas feed up to the airing cupboard and a flue up through the loft and out through the roof. This means we get hot water on demand and then have more flexibility over the heating control system. Many only control heating as you will see in the following list of device options. Moving to a combi boiler would also require every radiator in our home to be fitted with a thermostatic radiator valve.

Control Options

British Gas

Hive Active Heating enables control of both the heating and your hot water.


Hive hub
Hive uses a broadband connected gateway or hub, which uses ZigBee to communicate with other components. We wanted to avoid another hub and wireless technology in our home if at all possible. It requires both a spare Ethernet port and a free mains power socket.

This is yet another solution that requires a cloud service and subscription in order for it to work. We are simply not prepared to give such valuable data to a 3rd party service provider.


Hive receiver
Hive uses a broadband connected gateway or hub, which uses ZigBee to communicate with other components. We wanted to avoid another hub and wireless technology in our home if at all possible.


The thermostat module is battery powered and can be placed anywhere in your home.


  • Hive requries a cloud service and subscription to operate and shares valuable data back to British Gas.
  • Hive introduces another hub and another wireless (ZigBee) into our home.
  • It controls both heating and hot water but it only supports a single heating zone.
  • It has no learning capability and has no view of occupancy and presence.

Nest Thermostat

The Nest Thermostat is due to be announced in the UK soon. It is a popular device in the USA and some other countries, simply because it looks so good and is very well made. We have experience in using one (but not in our home).


  • Nest requires a cloud service and subscription to operate and shares valuable data back to Nest.
  • It doesn't really improve things as it is still a single thermostat placed in a poor location to provide useful heating control.
  • It only controls heating and will not hot water.
  • It is quite intelligent and even has limited occupancy detection.
  • It is expensive for a themrostat
  • It does look good and has a high gimmick factor.

Scottish Power

The Scottish Power Remote Heating Control provides a networked controller. There are iOS and Android apps to let you connect to your home and if you have no Internet access, you can turn your heating on or off via SMS. There is also an on-line portal to set schedules, adjust time settings and more. It costs £249; and it is claimed it requires no additional wiring and takes just 60 minutes to install. This is simply Scottish Power reselling the Climote system.

This device is not available in all UK locations (as it requires mobile phone network coverage) but, we passed the availability check.

Scottish Power Remote Heating Control controller
The Remote Heating Control controller supports more than one heating zone and hot water.


  • This is a controller only solution that uses your existing thermostat.
  • It can control two heating zones and the hot water.
  • It has its own mobile phone number and it can send and receive text messages.
  • This mobile data link is used for all control and has an associated recurring fee.
  • It has no learning capability and has no view of occupancy and presence.

We have ruled this solution out because it is SIM-based and after the initial 12-months is up, it has a recurring monthly fee. There is no option to use Wi-Fi or other networking technologies.


Remote Heating Control.


  • Tado is a heating only system and does not control hot water.


The advantage of a Z-Wave based solution is that we have a Z-Wave gateway, controller and network in our home already. It would thus be relatively easy to integrate this with our Home Control System (HCS) and take account of things like occupancy. We could also add intelligence and learning. It would not be a stand-alone, off-the-shelf solution though.


Horstmann / Secure SSR302
The simplest change we could make is to use a device like the Horstmann / Secure SSR302, to replace the existing controller. They are both electrically identical. This device is effectively a 2-channel Z-Wave switch.

This device would allow us to use our VeraLite to determine when the hot water and heating came on. In reality our Home Control System (HCS) would do this with much more intelligence and simply use the Veralite as a gateway to this device. Internal circuit of this device is identical to that of the LP241. This simple update would also allow us to use the existing wired thermostat is we wanted to.

Solid-State Relays

Solid state relay
In our next home we will use a wired solution using solid-state relays. The 12V dc control signals from our Home Control System (HCS) will be used to switch 230V ac power to the boiler and pumps.


Horstmann / Secure HRT4-ZW wireless thermostat
The SSR302 is designed to also work with the Horstmann / Secure HRT4-ZW (also called the Secure SRT321) wireless thermostat using the Z-Wave mesh network or directly linked by association.

It looks almost identical to the HRT4-B (pictured) but uses Z-Wave to communicate wirelessly and is not wired into the mains power. Because it is a battery powered Z-Wave node, it does not act as a relay node and can not be directly updated. The device will have to poll to collect updates from the controller, introducing a delay.

The only real advantage of a wireless thermostat like this is that you can remotely set the target temperature. This is something we have never needed to do, despite the clever marketing by companies selling smart thermostats. Basically, you set it and then leave it alone. In fact, is is actually desirable to not have family members and guests playing with your thermostat settings!

Radiator Valves

There are Z-Wave enabled thermostatic radiator valves and these would allow much greater levels of control. Thermostatic radiator valves are battery powered, though battery life is claimed to be pretty good. Because these devices are battery powered they cannot be polled and new values can only be sent to the valve controller when they report in.

The Decision

We eventually decided to replace our boiler without major modifications to our heating system. We also decided to replace the existing basic controller and replace it with the Secure SSR302 Z-Wave 2-channel receiver. We also decided to update our old thermostat with a battery powered Z-Wave thermostat.


SSR302 First Impressions

The SSR302 feels a bit plasticky. The front cover is opened by pushing the exposed lip to the right. The 'hinge' holding it on to the main body is a bit flimsy. The device comes with a universal backplate and we used this to test the device.

Some of the information available on the Internet claims the supplied manual shows an incorrect view of the internal wiring but, the manaul supplied with out device (Leaflet number P84154 - Issue 3) is correct.

Testing The SSR302

Testing the SSR302 as we have outlined here means working with mains wiring and voltages. These will kill you if you don't know what you are doing. If in doubt get a qualified electrician to install devices like this for you.

Horstmann / Secure SSR302 internal circuit
There is a good guide on this device on the Vesternet website. Internal circuit of this device is identical to that of the LP241 (image from Vesternet).

In order to test the device, we connected it up to mains power and connected some neon indicator bulbs between neutral and pins 3 and 4.

Including The SSR302

The steps required to include the SSR302 on to the Z-Wave are:

  • Install the SSR302 into your electrical system. In our case we did this in a test environment, whilst we evaluated the device.
  • Switch the power on.
  • The LED on the front of the SSR302 will flash red, indicating that it is not included in a Z-Wave network.
  • Move the Vera close to the SSR302 and put it into inclusion mode.
  • Press and hold both white buttons on the SSR302 until the LED starts flashing green (this should take 2-3 seconds).

Once included, we could see the parent device and 2 child devices via the UI7 interface:

UI7 view of the SSR302

Only the 'Heat' and 'Off' buttons in the UI do anything. The 'Heat' button on the parent device switches on the hot water only.

The LED on the SSR302 is now a steady orange colour in normal use. It flashes each time a command is sent to it.

This is a video showing the testing:

We plan to test the device like this for many weeks before it gets proprely installed, to ensure we get the right behaviour and reliability. This enables us to fully test out our presence and occupancy based control model.

Fail Safe Mode

The SSR302 receiver has a 'fail safe' mode, operating on both channels, which prevents the receiver staying on if it loses contact with a wireless thermostat. Every website we have read says that the receiver should only enter this mode when the channel is on but, this is not our experience. When we left the receiver alone with both channels off we came back to find the front LED flashing orange (which signifies fail safe mode). It will switch off both channels after about 60 minutes but it will always enter fail safe mode as well, regardless of how the outputs are set.

In normal operation the wireless thermostat sends a signal to the receiver channel that it is associated with every 45-50 minutes. If the receiver channel does not receive this signal, the receiver will go into 'fail safe' mode after 60 minutes.

This means we have to use a wireless thermostat or we have to send a 'heart beat' control signal to keep the heating or hot water on. This is very easy to achieve in our software and it could also be done using a scene on the VeraLite.

We have basically added a scene that runs every 29 minutes (all our scenes run at intervals that are prime numbers) and reads the database to get the current value and sends an HTTP request to the Vera, to set the channels to the current state. This means the SSR302 will not go into failsafe mode, even if one update fails. This is done with an HTTP request of the form:


Our only concern with this approach is the Vera Lite unit itself. For things like this we have found devices that are associated (e.g. our Everspring ST814 & Fibaro FGS221scenes on the Vera to report when the Central Heating and Hot Water are set to Off or Heat (On). This gives our Home Control System (HCS) a view of these events so that it can control the devices and know that commands have been received and acted upon.

These events are also captured in our Home Control System (HCS) logs and update the database.

In Use

The SSR302 acts as a mesh relay node when powered up. This means it will help improve the coverage and resilience of your Z-Wave network.

In normal use, we shouldn't need to touch the SSR302. We have implemented hardware buttons to enable useful functions like a +60 minutues extension on the hot water.

Mobile App

Mobile app view of the SSR302
The view of this device in the mobile app also mirrors that in UI7. It is also shown as having controllable temperature but these buttons won't do anything.

SSR302 Manual Control

For manual control you use the top and bottom white buttons along with the green and red buttons:

  • Turn On Heating (Channel 1) - Press and hold the top white button + press the green button.
  • Turn Off Heating (Channel 1) - Press and hold the top white button + press the red button.
  • Turn On Hot Water (Channel 2) - Press and hold the bottom white button + press the green button.
  • Turn Off Hot Water (Channel 2) - Press and hold the bottom white button + press the red button.


This is now a project in progress! We are now in the process of getting our boiler replaced.

It does look like we can achieve a lot of powerful automation and improve the heating efficiency though, for a very modest investment and not a lot of effort. The main reason why we would progress this is to test out some more ideas and the software that we are looking to use in our next home. We don't envisage a Z-Wave based system in our next home and would use direct wiring control to our Home Control System (HCS).

Learning For Our Next House

In our next house we are definately going to keep the hot water system and heating/cooling system separate. It simply makes no sense to have these things connected by a single boiler.

The hot water will be heated by both direct solar energy and stored electrical energy. There will be automation to enable/disable the electrical heating.

For the heating we require a fully zone-based control system in our next house. We will have the sensors and control to enable target temperatures to be set and maintained down to a zone level and we will also have the sensors to know when doors are open (zones have been connected together).

Unlike our current system, the heating will effectively be on all the time (when enabled) and the target temperatures will be intelligently controlled for each zone.

There will be automation to enable/disable heating and cooling and both will have a manual over-ride.

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