Good Afternoon All,

I am planning on ordering a temperature probe to test water temperatures in our premises. I have noticed that you can buy a simple water probe for around £20, however there are also fancy looking models which are 'rated' for Legionella testing and cost around £130.

My question is; is there a difference in what these fancy models do or is it just an excuse to put another zero at the end of the price? All it appears to do is show a digital reading of the temperature, which is exactly the same as the cheaper models do.

Any advice would be helpful as my company are currently on a cost cutting exercise and I will need some ammunition if the more expensive models are actually required.

Thanks all!

Edited by user 22 August 2018 14:08:08(UTC)  | Reason: Changed the text size from microscopic to readable.

I am using infra red thermometer. 

Never heard of 'probe wipes' neither!

As far as I know you put the probe in the water flow ...

Probe wipes are just single use antiseptic wipes as suggested – just cleaver marketing. Also like all alcohol wipes hand gels etc. they are not very effective against some bacteria (such as E.coli) – hot water is far more efficient at washing away bacteria. As others have said why would you worry about the probe being sterile when testing water you’re going to empty down a drain?  Have used infra-red probes in the past they are great for getting an instantaneous read out. For some reason I could never get an accurate reading when testing pipes that fed thermostatic controlled taps – always had to use a contact probe.

Chris, I too share your pain.

I see far too may "calibrated" sticky labels around the place, and as you so rightly say not everything used for measurement needs to be calibrated

You don’t need to use sterile wipes to test water.

You can get calibrated prob thermometers for 20 pounds don’t bother with IR as expensive and break.

Here is the Techsupp I provide.

1. Introduction

This technical supplement has been written to ensure the Thermometers calibration is still within working limits.

1.1 Requirements

Temperature measurement and control devices must periodically be calibrated in order to prove their accuracy over the full operating temperature range and according to the device’s data sheet definitions. Proven accuracy is mandatory because inaccurate readings can lead to serious risks. Some devices are covered by calibration certificates from the device manufacturer. These certificates are valid for a defined period of time and the associated devices may be used throughout this period without additional calibration.

However, there are circumstances under which proper device calibration or re-calibration

is needed. The list below is not comprehensive but illustrates some of these

circumstances:

• A calibration certificate is not available because it has been lost.

• The device is used for longer than the period covered by the calibration certificate,

either at the user’s risk or with the approval of the manufacturer.

• The device was used or treated beyond the manufacturer's data sheet limitations

(e.g. excessive temperature, shock, etc.).

• The battery powering the device was replaced.

• The device's measurements are suspect.

• The device manufacturer specifies that a calibration procedure should be carried

out at regular intervals.

1.2 Objectives

Ideally, calibration should be carried out by a nationally or internationally accredited

calibration laboratory with proven accuracy standards and appropriate equipment.

Wherever possible, calibration should be carried out in accordance with the device

manufacturer’s instructions, or by following a device-specific policy.

 2. Procedure: The ice-water bath provides an accurate reference temperature at 0°C if the melting ice -

water mixture is properly set up, handled and maintained. An accurate temperature is

achieved by this method because an ice-water mixture in a container which is open to the

atmosphere will stabilize at its own “triple point”. At this point all three aggregate states of

water coexist: liquid, solid and gaseous.

 2.1 Action:

Place ice into a small clean jug or container and add a small amount of water to just cover the ice. Ideally chilled water should be used, the water level should be enough to saturate the ice but not enough to float it. Place thermometer probe into the slush for at least one minute, taking care not to let the probe contact the container. If the thermometer does not read between -0.5°C and +0.5°C of the reference thermometer, adjust it to 0°C. Non-adjustable thermometers outside of the + or – 2 degrees will be removed from use until they have been professionally serviced. Thermometers that have required adjustment for 3 consecutive months should be replaced.

2.2 Calibration in hot water:

Heat a clean container of water to a rolling boil. Place the thermometer probe into the boiling water for at least one minute, taking care not to let the probe contact the container. If the thermometer does not read between -0.5°C and +0.5°C of 100⁰C, adjust it to 100°C. Non-adjustable thermometers outside of the + or – 2 degrees will be removed from use until they have been professionally serviced. Thermometers that have required adjustment for 3 consecutive months should be replaced.

3.0 Record:

Record all findings on the Thermometer Calibration record.

So, you also need an atomic clock as there was no tolerance given with those time periods :o)

I assume it fails the test if it takes 2 minutes and 1 second to reach temp.

Yes, ok I’m joking but the OP has a very valid question, so who has decided that a calibrated thermometer is necessary, the HSE in some guidance? or some learned body? don’t get me wrong if there is a need for that accuracy then fair enough, but is there or have we H&S people or some sales people done this to us.

As I said everything that measures whatever has a tolerance of some kind. Just because there are some legal requirements for control, does not make it a requirement to be calibrated. When did you last have the speedometer in your car calibrated and what is the tolerance (10%?), but a truck does get it checked periodically. Horses for courses.

On a similar but different accuracy matter did you know the HSE are developing a noise app for a phone! The comment from the HSE person was it will be good enough to see if you have a problem! Well I never.

The melting ice water and boiling water test is generally sufficient in order to demonstrate that thermometer X is capable of giving you adequate temperatures. That's good enough and doesn't need to be an expensive thermometer (although those ones may last longer).

Once > +/- 1 degree then get a new one if cheap or adjust/formally service if expensive. :)

As an aside, regarding times on tap tests, even the 1 / 2 minute thing can be a misnomer.  Really hot water in a small vessel serving a small basin could be reasonably exhausted in 45 seconds giving an unrepresentative reading at 1 minute.  Equally an OK reading at 1 minute could miss a problem when system actually should be hot enough within a few seconds on a functioning recirculating system...and so on and so on.

Cor.  Imagine if the real world looked different to standard tests?!

Hi everyone,

Sorry for the delay in replying and I'd like to thank you all for your input with this - I'm glad I'm not alone with the confusion! My initial thoughts were that the thermometers being sold with the 'Legionella testing' description were actually no more accurate than cheaper versions and Legionella testing was merely giving the manufacturers an excuse to bump up the price by £100...

However, if I was to purchase a cheaper thermometer for, say, £25, and carried out the ice/water test outlined by Thomo in his detailed reply, would anyone agree that this would be sufficient? As A. Kurdziel has suggested, I doubt that 0.5 degrees difference from the 20 & 60 degree targets would make a huge difference (but I'm definitely not an expert on Legionella!). I could even consider buying two separate models of thermometer/probe and compare the temperatures measured by each, but then I wouldn't know which one was correct! 

I'm trying hard not to over confuse the testing and over think what thermometer would be suitable for this, however I do know that I'll be asked to justify spending around £130 for something I can apparently get elsewhere for £25.

Clearly, £130 would be much cheaper than a case of Legionnaire's Disease...however I'm sure we've all been in the cost justification dilemma at some point! 

I use a £50 Thermapen probe thermometer had it 6 years comes with cert, never had it calibrated, great bit of kit just be careful of the probe as Ive stabbed myself a few times. do the ice and hot water every week to check.

Ha ha, I thought that was impressive looking text!

If you are checking it in ice and boiling water, then I would say you are calibrating it.  Not sure I'd want to do that as often as every week though.

Oh I see - that does make sense.

Originally Posted by: chris42

Just checked hsg274 and no mention of the word calibration. Interestingly the sites selling them for this purpose offer then with and without calibration certs. you can buy 5 cheap ones for the cost of a calibrated version. so are we saying the self test noted above with ice  etc and boiling water the other end is acceptable ?

I belive Xavier has said in the past they worked for the HSE, if so when you visited a company would you have expected to see a calibration cert ? or a self test record ? or nothing ?

Not the HSE, but certainly a regulator... and one who knows a couple of things about legionella and was involved in that string of documents you've mentioned there.

I'd be asking how the company could be sure the records were accurate. That certainly wouldn't need to be a certification certificate and if someone described to me the steam/melting ice water test and showed me they had undertaken it periodically e.g. some sort of self-test record I probably wouldn't push further than that - particularly if any checks I did myself tallied well with theirs.  No hard and fast rule as every investigation would be contextual to the situation.

We have a calibrated test unit in our lab that we use but obviously we'd be taking and acting upon measurements that need to be beyond reasonable doubt whereas any company just needs to show their monitoring and verification is reasonably practicable.  Different evidential test.