Seeking an accurate room thermostat

[tapped]

Hi All

We have a new build house which came built with a Glow Worm 15 HXi condesing boiler and Range Tribune tank pressurised system. The tribune came packaged with a Sunvic room stat and we are now on the third thermostat! Two have only been accurate to anything from 4-0 degrees away from the chosen temp (meanign a house too cold or too warm semmignly at random), and the third one we have had fitted needs to be set at 14 degrees to achieve a room temp of 22!

Can anyone recommend a reliable, precise stat I can use in place of this? a programmable one allowing different temps at different times would also be useful

Many thanks

Paul

 

[D_Hailsham]

Two have only been accurate to anything from 4-0 degrees away from the chosen temp (meanign a house too cold or too warm semmignly at random), and the third one we have had fitted needs to be set at 14 degrees to achieve a room temp of 22!

Can anyone recommend a reliable, precise stat I can use in place of this? a programmable one allowing different temps at different times would also be useful

What were you measuring the room temp with and how accurate is it?

Room stats are very dependent on location, the wall used, height, position relative to windows, doors radiators etc. Did you put the checking device right next to the thermostat or were you measuring the temperature in the middle of the room?

If you want a reliable and accurate programmable stat, I would recommend the Honeywell CM900 series which come in wired and wireless versions, 24 hour or 7 day.

You don't say which Sunvic you have but, if it is just a thermostat i.e. no time setting, and you have a conventional, not combi, boiler, you will need to retain your existing time switch to control HW times.

Read Honeywell Application Guides for more info.

 

[bengasman]

Roomstats are generally not calibrated, nor do they need to be. Just turn it up a bit if you feel too cold, or down a bit if you are too warm.

 

[D_Hailsham]

Roomstats are generally not calibrated, nor do they need to be. Just turn it up a bit if you feel too cold, or down a bit if you are too warm.

Maybe not in the past, when thermostats relied on bimetallic strips. But modern digital stats use thermistors of known accuracy and the circuitry can be designed to measure the temperature to within 0.5C, which is good enough for most customers.

As for whether the stat needs to be calibrated. Have you never met the customer who thinks that, if the radiator is cold (turned off by the TRV) then the room must be cold and so must they? So they go to the thermostat, look at it and find it reads 21. That must be wrong, they think and turn it up to 22C or 23C. Think what would happen if the stat read 14C when the actual temperature was 21C.

 

[tryingnottobeafool]

would you not be better off without it as your trvs do this for you

adjust the radiators

cooler in bedrooms warmer in living areas

 

[D_Hailsham]

would you not be better off without it as your trvs do this for you

adjust the radiators

cooler in bedrooms warmer in living areas

You are not trying hard enough

TRVs do not provide a boiler interlock.

 

[gas4you]

I always fit the Siemens programmable stats when fitting independant controls, you can calibrate them in the installer menu.

 

[bengasman]

Maybe not in the past, when thermostats relied on bimetallic strips. But modern digital stats use thermistors of known accuracy and the circuitry can be designed to measure the temperature to within 0.5C, which is good enough for most customers.

one of my digital thermometers measures 0.05 K accurate with certain probes, but is now almost 2 degrees out and needs calibrating

As for whether the stat needs to be calibrated. Have you never met the customer who thinks that, if the radiator is cold (turned off by the TRV) then the room must be cold and so must they? So they go to the thermostat, look at it and find it reads 21. That must be wrong, they think and turn it up to 22C or 23C. Think what would happen if the stat read 14C when the actual temperature was 21C.

exactly my point

 

[ChrisR]

Accuracy should not be confused with Resolution.
Some digi room stats resolve 0.1 C, but that doesn't mean they have any particular accuracy. Over a short period though they would give a Relative difference fairly accurately.

 

[Gasguru]

Is it wired correctly - you will get odd temperatures if the the anticipator resistor is not wired correctly.

Is the thermostat situated above a radiator/tv or other heat producing device?

Does it sit in direct sunlight?

Is the thermostat fixed to a stud wall or dry lined wall?

Is the cable fed through a duct?

Any air blowing through the back of the thermostat even the tiniest amount will throw the setting out seal with silicon sealer.

 

[Malc C]

I fitted a new digital thermostat to replace our old bi-matalic strip one. Its a Horsman and has 0.5 degree steps to set the on / off point. Next to it is an expensive barometer our parents bought us, and its thermometer matches the readout on the thermostat exactly.

The good point is that the heating system works really well, and if the temperature falls 0.5 deg C below the set point it comes on, and if it reaches 0.5 deg C above the set point it switches off !

 

[D_Hailsham]

As for whether the stat needs to be calibrated. Have you never met the customer who thinks that, if the radiator is cold (turned off by the TRV) then the room must be cold and so must they? So they go to the thermostat, look at it and find it reads 21. That must be wrong, they think and turn it up to 22C or 23C. Think what would happen if the stat read 14C when the actual temperature was 21C.

exactly my point

But not mine There are many who will believe what the thermostat says. So if it reads 14C, even if the actual temperature is 21C, they will instinctively think they are cold (it must be psychological) and turn it up to 21C. An absolute error of one or two degrees may be acceptable, but not six or seven.

 

[bengasman]

Is this what is known as the “customers don’t listen syndrome”?
I have given up trying to explain to people that it does not help turning up the trv when it is cold. 3 out of 4 places where you go in this with this sort of weather have the trv on max as they think it changes the rad temperature.
In essence, you are right. I just can’t be bothered with people who think they know better than the manufacturer.
And then, how many roomstats are located correctly?

 

[namsag]

RE trvs regular customer comment , i have that one at 2 and that one at 5 and rads feel the same temp.

Roomstats should be 1.5m from floor on an inside wall,out of direct sunlight and not above or 2 close to a heat source also makesure rad is not on the backside of wall in adjacent room.

And most importantly don`t check its accuracy with a thermometer your granny won at the bingo.

 

[Malc C]

And most importantly don`t check its accuracy with a thermometer your granny won at the bingo.

makes no odds if its a cheap or expensive thermomoeter, you can't change how mercury reacts to heat !