Ultima357

Well it sort of explains it and yes, you can calibrate the stats BUT.... my issue is that with a fully sealed passive house, merely stirring the air as you walk past can change the reading by 0.5 deg because in static air they are reading their own temperature. This little bit of air flow then gets it to read the actual room temperature. Rather than bodging the temperature reading by effectively calibrating the stats incorrectly, they should have a better designed housing that allows sufficient air flow up through the device to measure correctly. I could try to create a space behind them but in reality the back boxes are steel, screwed to noggins. Moving the insulation away a bit would just create a slightly larger space to heat. This probably would change the offset a little but wouldn't make them work as they should. I have drilled some extra holes in the top side edge of one and this reduces the self read offset to about 0.6deg. Probably needs another 6 across the top to be right!

Hi mvincentd. Yes we too have had a couple of instances where they self illuminate. How often they do it I don't know, it just depends if you happen to be facing them and only half asleep at the time. I've taken one fully apart, it's just the 4 little screws holding the pcb in so quite easy. I suppose you can put some nail varnish or tape over the leds if you want to. Having just come off the phone to Heatmiser and speaking with the guy who designed them, we went round in circles a lot, but basically he agrees that they a) do generate heat and b) this affects the sensor. This apparently is taken into account in the software algorithm and once calibrated, should be fine. But we couldn't really agree that this shouldn't be happening and that there wasn't enough air flowing through the housing to properly register room temperature. He claimed that my insulated stud walls were the problem but I pointed out that in all new builds, stud walls have to be acoustically insulated according to building regulations and therefore the stat has to work with these. So conclusion. All modern 230v stats with digital displays must generate heat because they have an inbuilt psu. Therefore any internal thermistor sensor is compromised unless there is very good air flow and a larger housing is therefore required. The modern sleek look just doesn't work and only solution is a remote sensor. We did agree on the fact that a remote sensor would be better at least.

They look like they'd have the same issue, poorly vented housing.

In reply to AliG, the issue with the MVHR is just that it demonstrated that the stats are guilty of recording their own temperature and do not have adequate airflow though the housing to be reliable. I get what you say about ignoring what they say and just get it comfortable but thermistor based digital sensing should not be this inaccurate. The dining one is near enough in the middle of the house, well away from the door to the hall. Our master bedroom one and all the others show similar results. When you look at the design of these stats, the thermistor is on the bottom edge, just below the tick symbol where the vents are. But there are no other vents, so any build up of heat has to come out of these vents or be disappated through the plastic body. The latter isn't much use of course. The remote housings are very well vented and do not exhibit this problem. QED. So therefore my findings hold true, they sense their own temperature and are very poor in sensing actual room temperature due to the enclosure and a brief puff of air just makes them erratic.

Peter. Just wondering if you have any recommendations of a better solution? Bearing in mind that it's 14 zones and Internet connected.

These, being a new build are all flush as you'd expect. They unfortunately have to be at 1200mm from floor level maximum these days to meet disability requirements in building regs, same as wall plugs have to be at least 450mm up from the floor. My remote ones use the Heatmiser housing and work fine.

The one in the photo is close to a worktop in the kitchen but they all exhibit the same issue. Take note though of the calibrated thermometer, the difference this reads between static and fanned air is just 0.2deg whilst the stat records 1.4deg. The self heat issue is a problem though as if you walk past a stat, the change in temperature easily triggers a call for heat and hence we do not get good hysterisis on the room temperature. Eg, sitting in our family/dining room which is 8.5 x 4m can feel chilly whilst the stat is sitting there reading around 23 deg. Place a thermometer by where your sitting or anywhere in the room and you find it's just around the 21 deg mark. Give a brief fan of air at the stat and it falls below 22 deg, so simply not achieving the right temperature. They are set to 0.5deg differential but are only really doing something like 2 degrees. And yes, we like the temperature at 23 deg, that's why we built passive. It only costs around £2 a day to keep it warm, all 253m2 of living area and warm attic space too ?.

In regards to the wiring centres, they are Heatmiser, the actuators are third party and the stats are the v2 model, 240v powered. I think the fact that the back plate contains the 240 to 12/5v psu (whatever the front panel runs at) is where all the false heat is generated. I'm frankly amazed that such a poor design gets to market and so widely distributed /badged by others too.

I have a Samsung ASHP linked via Heatmiser controls to a 14 zone, 21 loops UFH system. We commissioned this back in March 2020 just before lock down and after 1 week, it shut down as the property is passive insulated and triple glazed. Airtight too at just 0.17achr. Due to lock down delaying our finishing and selling the old place we finally moved in in September. Since the cold weather in early December I've been trying to get the heating system to work to our requirements. Initially sitting in the lounge and not being warm enough despite the Neostat showing 23deg, I invested in a calibrated thermometer and set about calibrating the Neostats to this. Property has MVHR too, so adds to the overall picture. This has now been nearly two months of adjusting but recently discovered that when the MVHR was switched off, the stats jump up in temperature value and records the house warming up overnight when the heating is off. So further probing found that the stats are recording their own heat. Front panel runs at 27 degs, the thermistor sensor on the bottom edge has no natural vents in the rest of the housing so with no air movement, the central heat of the stat just warms this up. Taking the stat off the wall I found the rear fixed plate running at 29 degrees. Top this all off with the fact that the bathrooms with remote sensors are fine and record the actual temperature and are not affected by MVHR airflow leads me to conclude that the Neostats are not fit for purpose. They generate too much internal heat to read correctly. To prove this I took one apart, drilled four holes in each side of the housing at the top and behold, it reads more accurately, now only 0.6 deg high with still air as opposed to 2 deg plus beforehand. The photos show the temperature with the stat given a gentle hand fan movement of air, still air without fan and the temperature of the face. The final one shows the drop in recorded temperature when. the MVHR cuts in. Note this MVHR is a Brink Flair 400 running at just 50m3/hr in this shot, the dining room being over 120m3, it is not the slightly cooler air hitting the stat directly as the dining room outlet will be serving up only about 6m3/hr but merely the stirring of the air stopping or reducing the stat reading its own temperature. So thanks for reading this far and just wondering if anyone has had head scratching moments with these stats? Going to try buying a decent looking remote thermistor and hooking it up just below the stat to see if this cures the problem and then seek redress through Heatmiser who have already suggested using remote sensing. Their suggestion rather reinforces my view of not fit for purpose.

Hi, Just finished and moved into my self build project. A 323msq single storey barn style dwelling built to passive levels. After a 5 year plus planning battle due to it being in a small village (hence outside of development zone) and in a conservation area, we finally achieved permission back in October 2018. Kicked off with my chosen frame supplier backing out due to financial woes but we eventually got underway in May 2019 and were just a couple of weeks away from completion at the start of 1st lock down. But that's life. Finally moved in after selling the old house in September last year. Now trying to fine tune all the systems, MVHR, ASHP, 14 zone UFH, etc etc. This is how I've come across this forum and hope that I can find out if anyone has come across the problem I am tackling with Neostat V2. I'll post this under another title so it gains more accurate placing in the forums.