Heating Project – How it fits together

This post is the second in a series, sharing the trials and tribulations of the “re-automation” of my home heating system.  For an introduction to the project, view the first post – The Idea.

We will look at the infrastructure of the heating system, I will include as many photos as possible and links to the products, so that you can view more detailed information, should you want.

The heating products

The system installed in my house is an integrated JG (John Guest) hybrid system. I say hybrid, as it consists of underfloor heating downstairs and conventional radiators upstairs.

JGTOUCHPAD. This is the central point of managing the entire system. It sits on a wired heating network as the master controller.  All the room controllers can be set via the Touch Pad through a reasonably easy to use touch interface.

JGSTAT v3JGSTAT v3.  There are two flavours:  In the kitchen is a PRTHW-N model, this is a room temperature controller and has the additional feature of managing the hot water.  The other 11 controllers are PRT-N models, which are exclusively room temperature controllers.  They all have a large LCD display with a nice backlit screen, slim fitting on the wall and easy to use. They’re not touch screen, you operate them via the grey buttons.

The JG UH1 is the point at which all the room controllers and the Touch Pad connect together.  It’s the equivalent of your internet router where all your devices connect to, difference being it’s all wired, not wireless.  Each room is considered a “Zone”, there are only 8 zones available in the UH1. In my house the installer has put in two UH1s, one downstairs and one upstairs. The UH1 is also the point where the heating zone valves, tank stat and boiler enable are wired.  The UH1s link together via the communication bus, so they do talk together.

The UH1s, room controllers and touch pad are linked together by an 8 core CAT 5e shielded twisted pair cable.  Each room controller has a relay embedded within them, when the room controller calls for heating, the relay energises which activates the output valve for that zone in the UH1. It also activates the underfloor heating pump and enables the boiler on.  Upstairs, the concept is the same: each radiator has a valve which is switched by the room controller.

Discovering the system

The Touch Pad controller was installed alongside the room controller in Диктант. the kitchen/living room. Unfortunately this was 4ft off the ground, so my first task was to move the Touch Pad to standing eye height.  After many hours of cutting holes and routing cables, I finally had the Touch Pad mounted where I wanted it.  Unfortunately, when I powered the system back on, the low voltage fuse blew in the UH1.  I triple checked everything and there weren’t any obvious issues.  It was a Sunday night in winter and I had now managed to take out the entire heating system, which didn’t go down well!!

To cut a long story short, after purchasing some low voltage fuses from the ever dependable Maplins; plus many hours of belling out cables with a multimeter, I discovered a short in two cables. They must have been sliced during the orignial installation. When the wiring was disturbed, this caused the cables to touch and short circuit, blowing the fuse.

Inside the JG Touch Pad

The internals of the of the JG Touch Pad look like this:

JG TouchPad

The photo shows the reverse side of the Touch Pad, the touch screen is face down. The green socket in the middle is the main connector that plugs into the backplate, mounted Heating onto the wall.  As an interesting point to note, the touch pad utilises a Samsung ARM processor.


I spent some time Googling “JG protocol” and a range of variations, to no avail. It seemed that nobody had actively reverse engineered any of their protocols.  I was beginning to believe that it must all be propriety and that it was going to take hours of researching to work out how the system communicates between controllers.  Thankfully, what you see in the photo above was my saving grace. You may notice underneath Illicit the left-hand vertical golden ribbon some white text which reads “HEATMISER“.


After some Google searches with various terms for Heatmiser, it turned out that Heatmiser are the manufacturer of the JG products. JG have re-branded and modded the products to suit their requirements.  They still share the same product variant names, for example “Heatmiser UH1” and “JG UH1”.  The best part of this discovery were the droves of developments available for the Heatmiser products. The highlights of what I discovered were:

  • The controllers communicate via an RS485 network.
  • The Touch Pad is the master node (as expected).
  • The comms protocol was published online (so I thought, at the time).

The first thing I needed was the ability to link into and communicate with the network, so I bought one of these:


It’s an RS232/RS485 to WIFI converter. What is essentially does is makes it easy to view the raw communication transmitting on the heating network. I will discuss the network communications and protocol in a future post.

The Connections

Touch Pad

ConnectionsThe connections for the cabled network are very straightforward.  The +/- points are the power connections.  The UH1s provide a 12v DC supply via two of the cables, in my setup, the installer has used the Orange/Orange-White cables.  The Y/B connection points are the RS485 network.  Doeksen The C/D connection points seem specific to the Touch Pad, as none of the other room controllers have the C/D connections.

Room Controllers (JG Stat – 11 x PRT-N and 1 x PRTHW-N):

The PRT-N controllers, which are in 11 of my rooms, have:

  • +/- power connections (12v)
  • Y/B RS485 network connections
  • A1/A2 relay connection Monkey point

The additional A1/A2 connections are from the output of the controllers switching relay.  You could, in theory, put a conventional switch here (on the UH1 side) and switch the zone on and off.

The special PRTHW-N, which also controls the hot water, has an additional B1/B2 connection.  This is the output Miami Dolphins Jerseys from the hot water demand relay, within the controller.

The Engine Room

In a conventional system, each radiator links up from a heating loop which runs around the house.  In my system, every radiator links back to two central points.  There is an upstairs distribution cupboard, “the engine room”, and a downstairs cupboard too.

Here’s what the upstairs cupboard looks like:


Looks impressive doesn’t it?  What you can see is the UH1 at the top, the white cables from the bottom of the UH1 are the wires to the zone valves.  The brass manifolds are the supply and return to and from the boiler.  The 9 cream cubes are the valves that control the flow of the supply to an individual zone. The zone valves are actually powered by a 240v AC supply, they’re either open or closed, based on the room controllers demand.  The silver metal box is a two port control valve that isolates the manifolds when no demand exists, I’m not entirely sure on the logic of this, as with all valves closed, there would be no flow, possibly over design?

The orange and white tubular units are the heating manifold flow regulators.  The length of the pipe to each radiator will vary from room to room, to compensate for this, the installer would balance each zone flow rate using these units.

A closer look at the zone valve and flow regulator:

Zone Value and Regulator

The heating philosophy

Every room controller has a time schedule for when that specific room does and does not require heat.  The controller is actually capable of maintaining two types of schedule: a 7 days schedule or a weekday/weekend schedule.  Within each day, there are two periods available to provide heating.  The first is the “Wake up” time, the ON time, and the “Leave” time, the OFF time.  The second schedule is “Return” time (ON) and the “Sleep” time (OFF).  When the controller switches between the ON and OFF schedules it switches between a user defined low temperature and a comfort temperature.

My controllers are limited to the simpler Weekday/Weekend  (5/2) schedule, this is a limitation of the Touch Pad, as it only supports this type of schedule. During the OFF schedule I don’t normally want the boiler to come on other than for frost protection, generally I find that 15°C is a safe limit and very rarely will a room get this cold, even in winter.  The only exception to this is bedrooms overnight; clearly, if a bedroom temperature dropped to near 15°C it’s not going to be comfortable, therefore the bedrooms are set to a minimum of 19°C.

You can program these schedules directly on the room controllers, with some intricate key pressing, or more simply on the central Touch Pad controller. Either way, the schedule is stored in the individual room controller, which I like, as it provides a degree of redundancy.  The Touch Pad controller provides the cheap jerseys added benefit of centrally managing the system, you can copy-and-paste schedules between controllers, set “Hold” temperatures for groups of controllers, so on and so forth.

One of the overall benefits with this type of setup is that the heating is only provided to the rooms that request it.  Therefore, if you want heat in only one room in the entire house, you’re not paying to heat everywhere, this strategy is more energy efficient and cheaper to run than conventional system.

In summary

We’ve reviewed the components in the heating system responsible for the control side.  I’ve omitted wholesale jerseys discussing too much about the boiler, pumps and the design of the physical system, but there is an article here if you’re interested (bear in mind it’s a conventional system in the article).

Every controller stores its own schedule.  If the current schedule period is in an “ON” period and the room temperature is less than the set temperature, the relay in the controller activates.  This switches the relay in the UH1 which opens the zone valve for that room.  The UH1 then opens the manifold valve, switches on the circulation pump and then enables the boiler.  The boiler regulates the flow temperature based an a separate control system.  Once the room is up to  temperature the reverse happens: The relay de-energises, this soodustus closes the zone valve and if no other zone is calling for heating, motors the two port valve closed, the “boiler enable” is set to OFF.

In the next article we will discuss “Tapping into the system” which will detail the specifics of understanding the communication protocol of the system between the Touch Pad and room controllers.

Stay tuned!

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