Network Protocol document

I have a 12V network of slimline thermostats connected through to a NetMonitor - which is now playing up. I have a vague plan to replace the NetMonitor with a RaspberryPi solution, which would also allow me to add features such as logging temps from the stats, demand, boiler cycling, etc. - all very exciting (not!). It's possible there are others out there who would be interested in such a solution, especially as Heatmiser, in their wisdom, have discontinued the NetMonitor and not replaced it!!!

Anyway, to progress I need to understand the thermostat protocol used on the network: when I installed the system (7 years ago) I had a document which described it - down to the packet exchanges, etc. Now I can't find it nor does it appear to be in the Heatmiser support pages. Anyone got it or can point to it?

Many thanks, Neil.

10 replies

Hi All

Just joined the Heatmiser forum - I tried the Home Assistant approach but, like other people, couldn't get it to work.  Has anyone had any success?

Hi Neil,

Yes I'm interested in your (dead) Netmonitor! Let me know how you want to proceed,

Take care 


Hi Neil

Have you looked at https://home-assistant.io/components/climate.heatmiser/ as this is the direction I am taking.  Have just got home assistant up and running on a pi so next steps are a suitable RS interface and I was planning on the below. 


Would i have to disconnect the touchpad I have in order for this to work, or can they work in parallel?




Thanks for the pointer to home-assistant - I'll definitely take a look.

This is what I've got hooked up to my Raspberry Pi:  https://www.sparkfun.com/products/retired/13706 - though this one looks OK: http://www.ebay.co.uk/itm/RS485-Serial-Port-Adapter-Module-TTL-RS-485-Arduino-Raspberry-Pi-/142131756971. Both use the Pi's on-board serial interface and can be packaged quite neatly. I'm looking to take 12V out of the UH-1 for power so I'd have an enclosure with the Pi, RS-485 interface and 12-5V regulator with only the stat network wires and Ethernet sticking out. It also removes the need to have a PC/laptop dedicated to the task.

You can get the touchpad to work in parallel with another network 'master': I don't have the touchpad but looking at the installation instructions (P43 here: https://www.heatmiser.com/en/download/153/network-products/5308/tft.pdf) it appears the recommendation is to hook up to connections C & D of the touchpad (as per the NetMonitor) instead of Y & B - I'd guess is to prevent contention on the network wires. In theory you could just connect to Y & B anywhere on the network but you might get unpredictable results if both 'masters' try to talk at the same time. Still, looking at the protocol I'd say it's quite unlikely you'd mess anything up, just have some failing messages you'd need to resend.

Cheers, Neil.

Hi Mark, unfortunatly the dead net monitor was binned late last year :¬(

I haven't moved any further forward with this specifically, but I have in the past weeks been playing with Home Assistant, having bought a pi, and they have a Heatmiser component that I think should work, but requires investment in a RS232 -> RS485 converter so I haven't started yet.  Am enjoying tinkering with Home Assistant though!

Cool, when you get a solution I wold be happy purchase your software and solotion.

Look at the heatmiser site it would be around £800.00 to undate to there current solution for us and you never know, maybe the next day it becomes obsolete!

Wishing you well with your good works :¬))

Hi Neil,

I see your post is year old now, so hope you are still around.

Our Net monitor has now failed, so was wondering if you found the anwers you require and have you Pi up and running?

If so is your solution available to share?



Hey Graham,

If you are interested in selling your dead Netmonitor I'm interested!




I still have my dead NetMonitor if you still need one...

Neil / James / Mark

Seems like we are in same predicament! !!

Have you had any joy in getting the Raspberry Pi controller going?

I would be interested in helping with this

Let me know and we can take this offline. 


I've got as far as adding an RS-485 interface board to the Pi (can dig out the make/model if anyone's interested) and creating a simple script which pings each stat to extract the data - though I haven't spent much time on it.

As well as providing a webpage interface to control everything what I'd like to aim at is for the Pi to poll the stats regularly and gather information such as real and set temp, calling for heat, etc. I'm also keen to get the time of the stats reset with the real time every day and they drift LOTS.

If there's lots of interest I agree we should set up a separate thread or discussion elsewhere.

Yes I'd be very keen know more....I never went as far as buying the netmonitor but would love to now be able to connect this up to a pi

Hi if you look on line for heatmiser rs485 protocol you will find if not tried it yet, looking to make something to take advantage of solar power with heatpump thats controled by a PTS-NTS. Idea is to read the "Return" temp and set the "Set" early to make use of free power

EXTREMELY interested! Whole reason I installed the 12V thermostats was with a view to adding Netmonitor - and just after I'd got them installed it was discontinued..