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. 
 

 

[sh_1986]

Hi

thanks for your reply! 
 

I decided to take a punt so ordered it. Heatmiser sent me a battery tray for a different neostat so after complaining they did actually send the part I’d ordered. 
 

I am pleased to report it does work!  I had to transplant the board into my old housing as they’ve changed the design of the little square nut for the bottom retaining screw for a nut moulded into the plastic with a round shape which clashes with the v1 stat itself. The rest of the housing is the same and the board slotted straight in. Been up and running successfully for over a week now. Might order a couple more for future use as I bet the others aren’t far behind. It’s interesting regarding the failure being related to heat - the one that failed is recessed into an upstairs stud wall and another I have of the same vintage downstairs is into a brick wall in a much cooler location! 
 

if the old board is of use before I chuck it please let me know. 

[SteveTheRepairman]

Glad you found a solution. That information could also help a lot of others. The units are made in China and some components are of dubious quality. Heat definitely accelerates the aging process of the components but they will ALL fail eventually. 
 

If you would want me to repair and upgrade your PCB to use quality longer life components then it would work out to be slightly more expensive than the Heatmiser new unit (with their shipping). I charge £10 to repair and upgrade the board (unless it’s a complete gonna!) plus postage of £3.25 to return it. Of course you would need to post to me so it’s about £16.50 in all. Shame you are not local as that would save all the postage costs.

 

[Ultima357]

At the start of this thread, I posted the unsatisfactory temperate sensing of these units due to the heat from the transformer and came up with the modified spacer to improve it. Heatmiser never accepted that they had a problem. I don't know why, but I didn't think of a proof of this bad sensing until a heating system fault occurred last week when the Heatmiser system was turned off for a while during the fault correction (an unassociated ASHP issue).

 

The penny dropped when I looked back at the extended profiles of the various stats and found that despite a fairly stable temperature (house is large, passive and super airtight), once switched off the recorded temperature at restart was significantly lower than the powered temperature recorded prior to being turned off. Additionally, when turned back on, even though no heating was being input, the temperature climbed back up. NB, the study climb prior to being turned off was solar gain. 

 

To prove the point, the bathroom one is a remote head unit and unsurprisingly, temperature recorded across the power break was stable. QED Mr Heatmiser! 

Edited Tuesday at 23:18 by Ultima357

[Kelvin]

I noticed the temperature over reading not long after we powered everything up. I have Loxone touch switches in each of the rooms with a Neostat and there’s a 0.7°C - 1°C degree difference between the Loxone reading and the Neostat reading with it being higher. I also have a Ruuvi sensor and it matches the Loxone sensor. 

[JohnMo]

9 hours ago, Ultima357 said:

despite a fairly stable temperature (house is large, passive and super airtight

So why do you need all these thermostats then?

 

Not sure I have a read a single thread on here where anyone says Heatmiser are good, generally misreading, failing or not communicating.

[Ultima357]

36 minutes ago, JohnMo said:

So why do you need all these thermostats then?

 

Not sure I have a read a single thread on here where anyone says Heatmiser are good, generally misreading, failing or not communicating.

The UFH is divided into 14 zones and something has to tell it to switch on is the reason for room stats. With MVHR too, and being super sealed (0.17ach) and the thermal performance, individual rooms can change considerably with solar gain, so we need that level of granularity in control. Doesn't seem to be any other system that challenges the Heatmiser/Neostat either unfortunately. 

[Ultima357]

1 hour ago, Kelvin said:

I noticed the temperature over reading not long after we powered everything up. I have Loxone touch switches in each of the rooms with a Neostat and there’s a 0.7°C - 1°C degree difference between the Loxone reading and the Neostat reading with it being higher. I also have a Ruuvi sensor and it matches the Loxone sensor. 

Well you can calibrate the Neostat to match if you want to. I used a reference thermometer. And yes, there's no real alternative to the Heatmiser system, so we are stuck to make the best of it. 

[JohnMo]

8 minutes ago, Ultima357 said:

The UFH is divided into 14 zones and something has to tell it to switch on is the reason for room stats. With MVHR too, and being super sealed (0.17ach) and the thermal performance, individual rooms can change considerably with solar gain, so we need that level of granularity in control. Doesn't seem to be any other system that challenges the Heatmiser/Neostat either unfortunately. 

Are you running high flow temperatures in thin screed. If not your floor will self regulate. In a low energy house, the floor temp is only going to be 1 or 2 degrees warmer than the room, most of the heating season. So solar gain naturally shuts down floor output. No need for a thermostat to do it for you. A floor surface that is at or equal to room temperature has zero heat output. A room that is warmer than the floor surface, the actually sucks heat in. If the floor loops are circulating this heat is absorbed by the heating water and redistributed around the house.

 

We also have a similar house (we get massive solar gain in the shoulder seasons) we dumped the thermostatic micro managed system an age ago. Works way better without it.

[Kelvin]

1 hour ago, Ultima357 said:

Well you can calibrate the Neostat to match if you want to. I used a reference thermometer. And yes, there's no real alternative to the Heatmiser system, so we are stuck to make the best of it. 

I calibrated them all but I stopped using the thermostats per room to manage everything a while ago. 

Edited Wednesday at 10:21 by Kelvin

[Ultima357]

3 hours ago, JohnMo said:

Are you running high flow temperatures in thin screed. If not your floor will self regulate. In a low energy house, the floor temp is only going to be 1 or 2 degrees warmer than the room, most of the heating season. So solar gain naturally shuts down floor output. No need for a thermostat to do it for you. A floor surface that is at or equal to room temperature has zero heat output. A room that is warmer than the floor surface, the actually sucks heat in. If the floor loops are circulating this heat is absorbed by the heating water and redistributed around the house.

 

We also have a similar house (we get massive solar gain in the shoulder seasons) we dumped the thermostatic micro managed system an age ago. Works way better without it.

We are not thin screed. The entire house sits on and in 150 - 300mm of polystyrene, so the UFH pipes were cast into the slab, effectively a 155 ton thermal mass. This greatly improves the temperature stability. Floors are largely carpeted with suitable low tog underlay and carpet because that's what we prefer. If we run all loops at once, this is not effective or efficient as with 1.5km of pipes, it's quite a substantial system, (253m2 single storey BTW). So individual room control is very desirable and was part of the design, especially as we keep some cooler than others. By controlling when/where we heat, I can use the 6 hrs of 7p/kwhr overnight rate to maximum benefit, topping up during the day from battery and then grid when battery is exhausted.

 

Overall, our average cost is sub 12p/kwhr and the cost of heating & hot water has averaged £227 per year over the last 3 years which is I'm sure you can agree, pretty much perfect. We run at 23deg in our active rooms and 22 in others, plus the 140m2 of warm attic as insulated at roof level in the main part of the house (400mm Warmcel). On really cold days, the rooms will heat cycle around once an hour maximum, mostly closer to once every couple of hours which is acceptable I think. 

[JohnMo]

Sorry with all that concrete in the floor I have no idea how the thermostat affects anything. You really are only opening and closing zones to keep some flow circulation through your 20+ loops at a sensible rate.

 

17 minutes ago, Ultima357 said:

1.5km of pipes

Only 3x more than me.

[Ultima357]

21 minutes ago, JohnMo said:

Sorry with all that concrete in the floor I have no idea how the thermostat affects anything. You really are only opening and closing zones to keep some flow circulation through your 20+ loops at a sensible rate.

 

Only 3x more than me.

The thermostat senses the room temperature, operates the UFH zone valve to open/close the flow in that room. There are no sensors in the floor as it was impossible to cast them in the slab which was power floated to final finish on the day it was poured (yes, a long day, some 13hrs!) See photos. 

[Ultima357]

An answer from Heatmiser :-

 

The thermostats use a rolling average with an artificial temperature limit of 0.1 degree rise(or fall ) every 10 seconds. if you power the device down the rolling average is lost and the device starts with an average value of 0 there are 16 readings taken each time so the average quickly rises, the process then continues until it reaches equilibrium. So its not surprising that you saw a lower temperature just after powering the device on.  

 

The headless device remain powered so didn't lose its rolling average when the system was powered down. 

 

There is a second temperature sensor in the middle of the powered unit that monitors the power supply temperature, predicts the effect on the room sensor and compensates in real time.

Its not perfect but has been tested repeatedly in an environmental chamber whilst mounted on a plaster board frame with and without wall insulated behind the plaster board. 

The test results show that the measured temperature matches the chamber temperature within the specified +/- 1 degree or better.  

 

I've pointed out as I did originally, that it is a building regulations requirement for noise reduction insulation to be fitted in stud walls and suggested they retest with insulation. 🤔

[Alan Ambrose]

>>> Not sure I have a read a single thread on here where anyone says Heatmiser are good

 

I've two set-ups that have been working well for years. These are wired. There is the odd software bug, the bug/feature request 'forum' is a bit 1984, I found the relays are a bit cheap and downrated and the physical design is a bit flimsy in parts. But I'm pretty critical of any product.

 

It does allow us to have a schedule on each room, to set rooms to schedule or standby, a holiday setting (all off except frost protection), remote access etc. I even have a stat in my shed running a blow heater that I can set going in winter sometime before I do some work😁. And Heatmiser don't upgrade the xxxxing software every 5 minutes.

[Kelvin]

31 minutes ago, Ultima357 said:

An answer from Heatmiser :-

 

The thermostats use a rolling average with an artificial temperature limit of 0.1 degree rise(or fall ) every 10 seconds. if you power the device down the rolling average is lost and the device starts with an average value of 0 there are 16 readings taken each time so the average quickly rises, the process then continues until it reaches equilibrium. So its not surprising that you saw a lower temperature just after powering the device on.  

 

The headless device remain powered so didn't lose its rolling average when the system was powered down. 

 

There is a second temperature sensor in the middle of the powered unit that monitors the power supply temperature, predicts the effect on the room sensor and compensates in real time.

Its not perfect but has been tested repeatedly in an environmental chamber whilst mounted on a plaster board frame with and without wall insulated behind the plaster board. 

The test results show that the measured temperature matches the chamber temperature within the specified +/- 1 degree or better.  

 

I've pointed out as I did originally, that it is a building regulations requirement for noise reduction insulation to be fitted in stud walls and suggested they retest with insulation. 🤔

I have umpteen ways of measuring the temperature in the room and they more or less all correlate whereas the Neostat tends to read higher although not all of them do it. 

[Ultima357]

27 minutes ago, Kelvin said:

I have umpteen ways of measuring the temperature in the room and they more or less all correlate whereas the Neostat tends to read higher although not all of them do it. 

You can calibrate the Neostat within the options menu to read the same. I used a reference calibrated thermometer to set mine up.