Heatmiser Neostat v2 temperature sensor problem

[Pyewacket]

I have had the same problem. AT about 9 years old one V1 Neostat PSU has failed. I managed to source a NOS replacement and all is well but I may try to ventilate the others to reduce the chance of failure (if this is indeed the cause). Of interest the transformer on the faulty PSU has minor discolouration suggesting it is the faulty element. The capacitors look ok but I’m not an electronic engineer so can’t test any of the components. 
If anybody can suggest where I could source a new transformer I could try to solder in

a new one. 
J

[Alan Ambrose]

I’m not sure that transformer looks bad. They just put a bit of tape over the windings to add a bit of insulation. If it’s pressed onto the windings it shows through more of the colour in the varnished windings. Most PSU faults are something going pop through stress or electrolytic capacitors leaking or bulging and losing their minds.

[SteveTheRepairman]

By chance I stumbled across this thread and found it very interesting. By accident I have been repairing the back panel PSU of Heatmiser neostat V1’s now for several months.

 

The background for this is that I built a large Scandia Hus property in 2011 with UFH on three floors. I fitted 24 x 12v networked Heatmiser PRTN style touch thermostats, touch pad and a net monitor to connect to the internet. This actually worked quite well until recently where the Heatmiser app is now just about useless on the iPhone latest IOS. So I looked at changing over to neostats with a neohub but there is no direct replacement for all the thermostat types that I have. In addition, the neostats look like a backward step in both aesthetics and function to the touch screen stats.

 

I purchased a neohub and some cheap faulty neostats from eBay (which I repaired) to investigate the Neo app and whether I could fake my existing system with HW/SW to operate with it. Unfortunately this turned out to be near impossible due to encryption of data packets using SSL and Heatmiser would not help me.

 

However, from my experience with the neostats, I do have a clear understanding of the PSU design and why it fails. I have repaired quite a few now  but use much higher spec parts than the parts that Heatmiser have assembled them with. The repaired PSU should last a lot longer than the original. If anyone wants their backplate repaired then I may be able to offer that service at a small cost if that sort of thing is allowed on this forum. 

 

I am now investigating a HW/SW solution to allow my legacy netmon based system to be used under Apple HomeKit via a home hub and hope to make good progress with that very soon. 

[Pyewacket]

Steve, thank you. Would definitely be interested in a preemptive fix. The V2 stats aren’t cheap!

Where are you based?

j

[Alan Ambrose]

@SteveTheRepairman >>> this turned out to be near impossible due to encryption of data packets using SSL and Heatmiser

 

Way back I controlled my heatmiser ufh controller from a custom-made windows app. Now it’s been replaced with a hub and different heatmiser controller and works fine with their app. But … the comms between the stats and the heatmiser ufh controller is standard rs485 - so hackable. Also there’s an api you can use to control the hub which you can use if you want. I’ll see if I dig it out.

[SteveTheRepairman]

On 13/03/2025 at 18:38, Pyewacket said:

Steve, thank you. Would definitely be interested in a preemptive fix. The V2 stats aren’t cheap!

Where are you based?

j

I am based near Leatherhead in Surrey, about 10 mins from the M25 J9 or J10. 
 

[SteveTheRepairman]

I have now repaired a lot of the V1 back panels including Pyewacket’s who posted above. One thing that is common is that as they start to fail, the linear regulator on the PCB starts to dissipate more power as the pre regulator voltage increases considerably. This generates more heat that will cause even more misreading of the actual room temperature. If you experience increased positive inaccuracy of temperature it is likely your back panel is on its last legs. Eventually the linear regulator also fails due to overheating like it did on Pyewackets PSU. Hope this may be of help to anyone.

 

[sh_1986]

just read this thread with interest. Have 2 x v1 neostat room stats, one of which went offline the other night. after switching the panels and backplates around I concluded one of the backplates has failed. 

I found that Heatmiser sell a V2 backplate psu as an individual part for £10 & postage although in the description it tells you only to buy it for v2 stats.

Heatmiser tech support also confirmed this and pushed me towards buying a whole new v2 stat (which I don't want to do as they have a different colour backlight and won't match the UFH neostats that sit directly alongside, also seems excessively expensive when it's only the backplate that's failed).

 

Earlier in this thread someone noted they had used v2 backplates with v1 stats and I've also seen an old ebay listing where someone sold a v1 stat/v2 backplate combo and said it was working fine. Can anyone confirm real life compatibility please? of course it suits Heatmiser to say it's not compatible because this will mean people can keep their v1 stats going longer using a £10 spare part 🙃

[SteveTheRepairman]

On 20/05/2025 at 09:57, sh_1986 said:

just read this thread with interest. Have 2 x v1 neostat room stats, one of which went offline the other night. after switching the panels and backplates around I concluded one of the backplates has failed. 

I found that Heatmiser sell a V2 backplate psu as an individual part for £10 & postage although in the description it tells you only to buy it for v2 stats.

Heatmiser tech support also confirmed this and pushed me towards buying a whole new v2 stat (which I don't want to do as they have a different colour backlight and won't match the UFH neostats that sit directly alongside, also seems excessively expensive when it's only the backplate that's failed).

 

Earlier in this thread someone noted they had used v2 backplates with v1 stats and I've also seen an old ebay listing where someone sold a v1 stat/v2 backplate combo and said it was working fine. Can anyone confirm real life compatibility please? of course it suits Heatmiser to say it's not compatible because this will mean people can keep their v1 stats going longer using a £10 spare part 🙃

Sorry, I don’t know the answer to your question but I see someone posted the same on the Heatmiser forum and was told they are not compatible.

 

I am amazed that HM only charge £10 for it. I don’t think I could buy all the parts for that! I can only assume they have an unreliability issue with them and want to keep their customers base happy by offering a relatively cheap fix. 
 

i see you are in Suffolk which is too far away for you to drop in (I’m in Surrey) otherwise I could have offered you a cheap repair service. I effectively re manufacture them replacing as a matter of course the components that age with higher endurance, higher spec ones that should last a lot longer.