Maximum Minimum Thermometers


How to read the thermometer

The minimum temperature is read on the left hand side – note red indicates below freezing point

The maximum temperature is read on the right hand side – black indicates above freezing point


Med maxmin thermometer 2.JPG

Current temperature

top of the mercury –   

     arrow 1 – 5°C


Minimum temperature bottom of left blue metal float –

     arrow 2 -2°C


Maximum temperature bottom of right blue metal float –

    arrow 3 – 21°C

To reset the max/min thermometer depress the central button (A) and allow the metal floats to decend to the top of the mercury miscus.  This might need a mild tap.


Common problems associated with a max/min thermometer

Broken beads of mercury – inaccurate readings.  Rejoin mercury by light tapping. 

Sometimes accompanied with “air” often rendering thermometer broken.

Mercury above the metal floats – arrow 1

This is very difficult to fix and generally the thermometer will be inaccurate and should be replaced.

Air bubbles within oil (multiple) – arrow 2

These also tend to indicate a broken thermometer



Breakdown of a maximum/minimum thermometer



Front A Thermometer B Magnet C Backing D


If the max/min thermometer indicates that there is a problem a digital temperature logger can be placed in the area and the records plotted on a graph against time.

The following is an example from a medicine fridge where normal expectations is 2-8°C: