Room thermostat reading high

[mattg4321]

I recently fitted a Heatmiser Neostat for a customer in their hall- to control their radiators throughout the house (70’s 4 bed medium sized detached).

Quite bizarrely the thermostat is reading 3 or so degrees above the actual temperature when the lounge/hall door is open. Ie stat shows 22, when it’s actually only 18/19 as per a separate standalone thermostat. You can ‘feel’ that the standalone thermostat is the one showing the correct temperature.

However, if you then shut the lounge/hall door, quite rapidly, within a couple or a few minutes the temperature on the Neostat drops to roughly where it should be and reads ‘correctly’.

I’ve fitted loads of these stats and never had this problem. I’m not convinced it’s a faulty unit, why would it be so easy to recreate the conditions which affect it (just by opening/closing an internal door)?

It seems like there is some weird airflow causing this, but no problems were apparent on the old Honeywell mechanical stat it replaced. If it was the internal electronics in the Neostat heating the unit up and causing the unit to overread, logically you’d expect this to improve when the hall/lounge door is open, not worsen! The long and short of it is that the thermostat seems fine with the hall/lounge door closed, but over reads when it’s open.

FYI the stat is mounted on a dry lining box into an internal stud wall fairly recently erected, that appears to have no insulation within it. I’m pretty certain there are no penetrations into this stud wall from outside the thermal envelope, but there will be one into the 1st floor joists space.

Any ideas anyone? Cheers in advance

 

[ferg]

You could try putting glass wool or similar through the cut out for the fast fix box as a draught excluder.
Probably a bit of a long shot but maybe worth a try.
Airflow was my first thought too so if you are wrong then I would have been too.

 

[brianmoooore]

I've come across many cases where wall mounted thermostats are affected by draughts coming from the cavity wall onto which it's mounted, or coming down a conduit from the floor/ceiling space, but surely this is the wrong way around for that? Draughts will cool the stat, so the room will be hotter than the reading on the stat.

 

[Rockingit]

I don't know that model of stat but some intelligent one's have a draft mode where it senses if there's been a sudden loss of temp and interprets that as a door open - so will shut down to conserve energy. Could be some flavour of that happening??