Thermostat showing too high temperature

jpsartre

So this is an odd one (to me at least). We've got a Worcester Bosch boiler (installed less than a year ago). This morning the thermostat was acting up and not responding very well. I changed the batteries and now it's working again but it's telling us the temperature is about 4 degrees above what it actually is. The thermostat is working (if I place it near a radiatior it goes up, in the fridge it goes down fast), it's just consistently 4 degrees above the actual temperature. Any idea how to fix it?

Gerry1

And how are you measuring the 'actual' temperature?

Talldave

Could it have previously been indicating lower readings because the batteries were going flat?

jpsartre

Gerry1 said:

And how are you measuring the 'actual' temperature?

Just by how it feels and what the thermostat used to show. Granted it's not an exact science but I can tell the difference between a room that's 19 degrees (as we usually have it) and 23 degrees.

jpsartre

Talldave said:

Could it have previously been indicating lower readings because the batteries were going flat?

I thought about that but it's been entirely consistent in the readings since we had the boiler installed about 8 months.

matelodave

I'd be interested to know how the "actual" temperature is being measured. Unless what you are using to check the temperature has been calibrated then you do'nt really know which one is correct - the thermostat or the thing you are using.
Just because something might be digital and reads out in actual numbers doesn't mean that it's accurate. have you checked whether your thermostat has a temperature offset facility.

jpsartre

matelodave said:

Just because something might be digital and reads out in actual numbers doesn't mean that it's accurate.

I get that and it may not have been correct before either. But it's definitely showing a much higher temperature than it did before and it's not correct. Even with the heating off most of the day (it's been about 14 degrees outside) I never saw it go below 23 degrees. At the end of the day it's not a big problem as we can just adjust the temperature we want accordingly, I was just a bit puzzled about it.

Not sure what a temperature offset facility is but the manual doesn't mention it (it's a Greenstar 30i boiler).

Talldave

I do wonder if it has an offset that's been cleared by a battery change.

As an example of how wide ranging temperate measurements can be, the Heatmiser thermostat in the room I am currently sitting says it's 23C, whilst a cheapish ebay digital thermometer with a dying battery is showing 28C.

matelodave

Offset is a facility whereby you can adjust the reading to compensate for any inaccuracy in the reading usually due to location or other external factors.
Calibration is where the device has been checked against a known and certified standard and any variation in readings has either been adjusted or a calibration chart has been produced showing the variation from the standard. This allows the display on the device to be corrected by adding or subtracting the variation figure.

Most stuff has a specified accuracy figure usually presented as a percentage and if it's digital within a +/- one or two digits as well.However consumer stuff like thermostats and thermometers can be miles out.

For example a thermomometer or thermostat that has an accuracy of +/- 5% could read anywhere between 23.7 and 26.3 when it's supposed to read 25.0

jpsartre

Thanks for that, you learn something new every day

Gerry1

matelodave said:

For example a thermometer or thermostat that has an accuracy of +/- 5% could read anywhere between 23.7 and 26.3 when it's supposed to read 25.0

Unfortunately not.  Otherwise a reading of 1º when it's 0º would represent an infinite error ! 

You'd have to use the Kelvin scale. </pedant>