Heatmiser Neostat v2 temperature sensor problem

[Temp]

Are any of the MVHR vents directly above the stat? If so I would adjust any vanes to point the air flow away from the stat and then recalibrate the stats. See how they work then.

[Ultima357]

3 minutes ago, Temp said:

Here is a photo of the remote sensor I built.  Just a small project box from Maplin with three holes drilled top and bottom and an NTC inside. Cant remember if its a 10k or 20k Ohm but it was in the manual for the stat somewhere.

 

 

and this is the old Heatmiser stat we have showing the vent holes. Same both sides and similar on the bottom. None on the top - probably to keep dust out?

 

 

Interesting. The old design looks sensible to me. The project box solution might be what I end up doing as I'm going to get some 10k ntc thermistors to experiment with. 

[Ultima357]

Just now, Temp said:

Are any of the MVHR vents directly above the stat? If so I would adjust any vanes to point the air flow away from the stat and then recalibrate the stats. See how they work then.

No. Mvhr vents are near the windows /furthest from the doors to achieve good airflow through all the room. None are adjacent to the stats, I deliberately designed it all this way to avoid that issue. My original experiment was just using a small paper fan in any case just to move the air. If you probe 20mm below the stat you read say 22deg, push the probe close but not touching the bottom of the stat and it reads 23 or higher indicating heat exiting the housing. In my drilled one, if you probe beside the new holes you read 24 deg... 

[Temp]

I know the self heating effect isn't ideal but the internal temperature of the stat should still track external changes in temperature provided they aren't subject to changing draughts from the MHVR or your desk fan.

 

I would try and recalibrate them then monitor to see how well they track your thermometer over a few days. Cheaper than replacing them all.

 

You don't actually want the stats to respond to short term fluctuations in room temperature because that causes cycling of the heating system. I have wax cartridge actuators that take several mins to open/close so fluctuations shorter than that are effectively ignored anyway.  So the fact that changes in room temperature take awhile to reach the sensor buried in the stat shouldn't matter too much. Obviously you don't want it to take hours to catch up but 10-20 mins shouldn't hurt.  

 

 

Edited January 18, 2021 by Temp

[Tabblink]

I have fitted loads of these myself. Do they not have a temperature offset adjustment within the settings?

[Ultima357]

In answer to the question ofdo they have offset, yes they do, but you still should not have to be calibrating a temperature monitoring device to account for its own heat source. With varying temperature and air flow this will always be a compromise on the true temperature readings. 

 

Temp. Yes mine have the same melting wax actuators. But I'm coming back to the problem with the offset. If they are affected by their own internal heat source, the variable volume output of the MVHR will change this offset. Eg, very cold days I turn the MVHR back to just 50m3/hr but after cooking I might boost it to 100 or 220 m3 to remove the smells. Similarly, when my dear neighbour lit a bonfire recently I turned it off completely. This latter action immediately starts all stats climbing higher and you end up feeling cool even though the stats say 22 or 23deg. If everything was stable it might just work but you shouldn't have to be juggling with offsets on a decent piece of equipment. After speaking to Heatmiser, I'm going to try one of their extra wireless sensors linked to the stat to do some testing and temperature averaging. Plus I will try remoting the thermistor. At present, I haven't seen any other device that looks like it would overcome this. The industry seems to be of the opinion that you live with it. 

 

2 hours ago, Tabblink said:

I have fitted loads of these myself. Do they not have a temperature offset adjustment within the settings

 

[MJNewton]

23 hours ago, AliG said:

I find mine sensitive enough that I have changed the sensitivity from 1C to 0.5C as I don't like the temperature falling 1C before the heating kicks in

 

You can improve things even better than that these days (for many years in fact). Digital stats with 'time proportion and integral' control algorithms don't wait for the temperature to dip above/below thresholds before doing something. Instead, when they are in their 'proportional' band (of, say, 2C either side of the set point), they will either request a proportioned heat demand signal to the heat source if that's available (eg a modulating boiler controllable via opentherm) or if like me you've only got on/off controls available they it'll use pulse-width modulation to synthesize the same effect eg if it calculates that it needs 20% heat input to maintain the set temperature then it'll trigger a demand for 2 minutes in every 10. Simple, reliable (it constantly self-learns) and - most importantly - extremely effective at maintaining comfort. I've had a Honeywell CM927 for 15 years now and once up to temperature I don't think it ever really moves off the set point.

Edited January 19, 2021 by MJNewton

[Ultima357]

On 18/01/2021 at 15:25, Temp said:

 

 

Odd things going on with this editor, can't seem to shift previous quote but in response to MJNewton, I appreciate your reply but I have 14 of these, in a meshed array to WiFi hub. At circa 166 quid apiece, changing them all out to honeywell is too eye-watering!

[MJNewton]

1 minute ago, Ultima357 said:

Odd things going on with this editor, can't seem to shift previous quote but in response to MJNewton, I appreciate your reply but I have 14 of these, in a meshed array to WiFi hub. At circa 166 quid apiece, changing them all out to honeywell is too eye-watering!

 

Indeed! For such expensive stats it's even more depressing the issues you're having. You might be more willing to accept compromises if they were cheap (even then I think I'd be surprised).

[JFDIY]

How often are you likely to need to change the individual room temps?

 

Just wondering if you can use the in-riom locations for a remote sensor and move the 'stats to the be next to the wiring centre at the other end of the cable?

 

Though you might be then into a calibration exercise due to cable length (resistance) shifting the remote sensor output.

 

You can get sensor enclosures reasonably cheap, bit like these;

https://evatron.com/enclosures/sensor-enclosures/en30w-sensor-enclosure/

 

[dpmiller]

You paid HOW MUCH???? each? Please tell me that's a typo...

[gc100]

Interesting topic. I have 12 of these in my new build. I should be moving in at the end of the month so will keep a closer eye on these. So far they seem to be working as I’d expect but I’ve not actually checked the room temp independently. I did used 45mm deep boxes mined.

 

[ProDave]

If you are comitted to them, then the only sensible solution is convert them all to remote sensor with the sensor just below them.

[Ultima357]

4 hours ago, JFDIY said:

How often are you likely to need to change the individual room temps?

 

Just wondering if you can use the in-riom locations for a remote sensor and move the 'stats to the be next to the wiring centre at the other end of the cable?

 

Though you might be then into a calibration exercise due to cable length (resistance) shifting the remote sensor output.

 

You can get sensor enclosures reasonably cheap, bit like these;

https://evatron.com/enclosures/sensor-enclosures/en30w-sensor-enclosure/

 

That is an idea, not sure how practical it is though. The sensor boxes look identical to the Heatmiser ones that they charge £6.50 for.... 

 

4 hours ago, JFDIY said:

 

On 18/01/2021 at 15:25, Temp said:

 

[Ultima357]

2 hours ago, dpmiller said:

You paid HOW MUCH???? each? Please tell me that's a typo...

That's the price I found on a quick search for the Honeywell unit, not the Heatmiser. 

[Ultima357]

 

1 hour ago, ProDave said:

If you are comitted to them, then the only sensible solution is convert them all to remote sensor with the sensor just below them.

I've talked Heatmiser into sending me a remote wireless sensor which you can pair with the stat, then either use that or average it with the stat. Ultimately though I think a remote head with every one is the solution until someone produces something more sensible. But, with 14 of these plus the hub, changing them out is not a cheap option. 

[MJNewton]

7 minutes ago, Ultima357 said:

 

I've talked Heatmiser into sending me a remote wireless sensor which you can pair with the stat, then either use that or average it with the stat. Ultimately though I think a remote head with every one is the solution until someone produces something more sensible. But, with 14 of these plus the hub, changing them out is not a cheap option. 

 

Might there be a cheap(ish) solution to be found by just concentrating on what these stats are really there to do - measure temperature. With so many zones I am assuming you are not using the timer/programmer functionality on each and every one? I am picturing a centralised controller that reads the temperature in the 14 locations and controls each zone as required in accordance with a common schedule. I don't know what off-the-shelf solutions exist for that or whether a roll-you-own approach based on something like Home Assistant would be better (certainly cheaper). Sure, for the latter there'll be a bit of a learning curve but the end result ought to be good.

[Temp]

Could get away without a box. You can get a third party sensor and mount on a blanking plate...something like.. 

 https://www.amazon.co.uk/BIlinli-Thermistor-Temperature-Sensor-Waterproof/dp/B07R7G1QJK

 

For £150 you could buy a 3D printer kit and some filament and print boxes with vent holes any pattern you want:-) 

 

 

[ProDave]

3 minutes ago, Temp said:

Could get away without a box. You can get a third party sensor and mount on a blanking plate...something like.. 

 https://www.amazon.co.uk/BIlinli-Thermistor-Temperature-Sensor-Waterproof/dp/B07R7G1QJK

 

For £150 you could buy a 3D printer kit and some filament and print boxes with vent holes any pattern you want:-) 

 

 

Would it even be possible just to drill a hole in the bottom of the existing thermostat housing so that just pokes out the bottom?  That would be a neat solution.

[Temp]

That ones probably too big to do that but there are much smaller sensors.

 

Only hesitation is that you probably shouldn't expose the wires as the stats are mains powered.

[Ultima357]

On 18/01/2021 at 15:25, Temp said:

7 hours ago, MJNewton said:

 

Might there be a cheap(ish) solution to be found by just concentrating on what these stats are really there to do - measure temperature. With so many zones I am assuming you are not using the timer/programmer functionality on each and every one? I am picturing a centralised controller that reads the temperature in the 14 locations and controls each zone as required in accordance with a common schedule. I don't know what off-the-shelf solutions exist for that or whether a roll-you-own approach based on something like Home Assistant would be better (certainly cheaper). Sure, for the latter there'll be a bit of a learning curve but the end result ought to be good.

 

These stats are very sophisticated. Each has multiple timers and temperature settings which can be set via a saved profile. Eg a bedroom profile can be applied to each bedroom saving programming separately. The app means you can do this all from the comfort of your armchair, monitor temperature and speed of change, set some of the parameters in the stats too. Being internet connected, you can do it from anywhere too. The stats talk to each other, forming a wireless mesh network which hooks into the neo hub and hence onto the internet. Each is wired to the multiway wiring centres which in turn control the UFH actuators and pumps. ASHP is therefore dumb, just responds to heat call. So overall, I'm very happy with the functionality. It also hooks into Google, Alexa etc, so you can control each room via vouse if it takes your fancy. Some screen shots below. 

[Ultima357]

7 hours ago, Temp said:

Could get away without a box. You can get a third party sensor and mount on a blanking plate...something like.. 

 https://www.amazon.co.uk/BIlinli-Thermistor-Temperature-Sensor-Waterproof/dp/B07R7G1QJK

 

For £150 you could buy a 3D printer kit and some filament and print boxes with vent holes any pattern you want:-) 

 

 

Plenty of thermistors available. I'm trying one just hung out of the bottom of one of them at the moment which seems to do the job. Like you say, I just need a neat housing to make it look OK. Temping with the 3d printing but just ordered a new toy, a 3 axis cnc router, so may try making something with that. It's accurate to 0.1mm.

[Onoff]

1 minute ago, Ultima357 said:

Plenty of thermistors available. I'm trying one just hung out of the bottom of one of them at the moment which seems to do the job. Like you say, I just need a neat housing to make it look OK. Temping with the 3d printing but just ordered a new toy, a 3 axis cnc router, so may try making something with that. It's accurate to 0.1mm.

 

If you can CAD up a model and provide an stl file one of us can print a prototype.

[MJNewton]

9 minutes ago, Ultima357 said:

These stats are very sophisticated

 

Ah yes, understood. Makes it all the more surprising doesn't it that they can do a great job with that bit but somehow bodge the temperature sensing side! 

[Ultima357]

7 hours ago, Temp said:

That ones probably too big to do that but there are much smaller sensors.

 

Only hesitation is that you probably shouldn't expose the wires as the stats are mains powered.

True they are mains powered, that's the whole problem. The front panel/thermistor is probably 5v so perfectly safe. It's the heat from the power supply which is behind in the back box that generates the heat. As my trial one hanging out of the bottom is looking good, I'm probably going to wire them in as airsensors, drill out of the back box and pop out below/beside the stat and contain in a neat housing. (I have stud walls, so simple enough). If anyone wants to know, they are 10k NTC thermistors that you need. A few quid apiece max. Less than a quid if you can wait for the slow boat from China.