vaillant vsmart reading wrong temperature

[GRhodie]

my vsmart thermostat has suddenly changed from 22 deg to 18 deg. i put it outside and it dropped to 7 - 0deg out - now back in and 40 min later only reading 15. separate thermometer say 21. is my thermostat broken/

 

[CountryFan]

How long are you giving it to change temperature?

 

[GRhodie]

it was over an hour. i have just taken the batteries out for 30 seconds and seems to be reading correctly but need to do more checks

 

[CountryFan]

Have you changed the batteries recently

 

[GRhodie]

no but will get some later. temp reading very sluggish