Temperature monitoring and legionella

[xanld]

Update: I managed to get a reading of 58 degrees! Perhaps the thermostat on the immersion was not fully in the max position previously. Telford are saying that the maximum should be 65, but given that the pocket temperature could be 4-5 degrees out, we're getting closer to the magic 65!

They're saying that the immersion could be faulty, and they'd replace it, but if only if after I've sent it back for testing and it's proven faulty.

So maybe this is now no longer worth worrying about. I've learned a lot about how to account for the discrepancy, more details on legionella, and the fact the immersion has a stat of its own which I think was previously set low. Plus I still can't account for a mystery 2-3 degrees, but maybe I can let that slide.

Also @MeldrewsMate suggestion of a 168 hour timer seems like an interesting bonus learning.

I'm still not sure whether it's an issue to have 22mm pipe out of the tank, reducing to 15mm only after it's left the loft and entered the bathroom, but perhaps this isn't a big deal either.

Thanks all agin.

 

[xanld]

Update: I managed to get a reading of 58 degrees! Perhaps the thermostat on the immersion was not fully in the max position previously. Telford are saying that the maximum should be 65, but given that the pocket temperature could be 4-5 degrees out, we're getting closer to the magic 65!

They're saying that the immersion could be faulty, and they'd replace it, but if only if after I've sent it back for testing and it's proven faulty.

So maybe this is now no longer worth worrying about. I've learned a lot about how to account for the discrepancy, more details on legionella, and the fact the immersion has a stat of its own which I think was previously set low. Plus I still can't account for a mystery 2-3 degrees, but maybe I can let that slide.

Also @MeldrewsMate suggestion of a 168 hour timer seems like an interesting bonus learning.

I'm still not sure whether it's an issue to have 22mm pipe out of the tank, reducing to 15mm only after it's left the loft and entered the bathroom, but perhaps this isn't a big deal either.

Thanks all again.

 

[MeldrewsMate]

You could of course buy a new immersion heater thermostat, probably cheaper than the alternative of doing without an immersion whilst Telford do their 'testing', and it's always useful to have a spare.

Wait what? This sounds amazing! A quick search for "168 hour timer" has yeilded no useful search results though. Do you have a link or make/model?

That's something you'd have to build yourself unless someone else knows better. I built one for my dad's solar PV diverter and it works very well, but mine is based on an addition to an existing Arduino based project with a software modification to go with it. Yours could be much simpler, needing an output from your thermostat (=tank has reached 60°C), a mains powered timer (=your week has gone by without getting to 60°C), and a seperate relay (=latch ON until 60°C has been reached)

The time delay T1 by something like this: www.ebay.co.uk/itm/393480531697?hash=item5b9d446ef1:g:bbkAAOSwZpRh29kB

I'm afraid I'm not very good with windows software, so drawing a sample circuit is beyond me. I've drawn it on paper and taken a photo; fingers crossed it'll appear here...
Essentially the live supply appears on T1 constantly until the tank contents reach 60°C. During this time the timer runs. When it gets to 168 hours (7days) relay contact T1/1 closes and energises relay R1. Its contact R1/1 puts power to the immersion heater until the temperature reaches 60°C and T1 is reset.
During the summer months the timer will be reset just about every day as the Sun does its work, during winter or after a long cloudy spell the immersion heater will be called into action using grid power.

 

[xanld]

Are you sure the element is actually drawing current when it is supposed to be on? Might the stat have tripped out - I cannot see the trip, but they are fitted with a resettable over temperature trip, to prevent water boiling, if the adjustable stat fails/jams/weld up it's contacts. Yes, that stat is set at the maximum temperature.

It definitely draws power below 50 degrees and stops above what I now think may be something between 58-63 degrees. It's supposed to go up to 65, but having discovered and adjusted the setting on the immersion, and had confirmation that the dry pocket is up to 4-5 degrees inaccurate I'm now inclined that any calibration issue on the immersion stat is relatively minor.

 

[xanld]

You could of course buy a new immersion heater thermostat, probably cheaper than the alternative of doing without an immersion whilst Telford do their 'testing', and it's always useful to have a spare.

That's something you'd have to build yourself unless someone else knows better. I built one for my dad's solar PV diverter and it works very well, but mine is based on an addition to an existing Arduino based project with a software modification to go with it. Yours could be much simpler, needing an output from your thermostat (=tank has reached 60°C), a mains powered timer (=your week has gone by without getting to 60°C), and a seperate relay (=latch ON until 60°C has been reached)

The time delay T1 by something like this: www.ebay.co.uk/itm/393480531697?hash=item5b9d446ef1:g:bbkAAOSwZpRh29kB

I'm afraid I'm not very good with windows software, so drawing a sample circuit is beyond me. I've drawn it on paper and taken a photo; fingers crossed it'll appear here...
Essentially the live supply appears on T1 constantly until the tank contents reach 60°C. During this time the timer runs. When it gets to 168 hours (7days) relay contact T1/1 closes and energises relay R1. Its contact R1/1 puts power to the immersion heater until the temperature reaches 60°C and T1 is reset.View attachment 269370
During the summer months the timer will be reset just about every day as the Sun does its work, during winter or after a long cloudy spell the immersion heater will be called into action using grid power.

100% amazing. One day I'll get my head around this and do it!

 

[dilalio]

100% amazing. One day I'll get my head around this and do it!

You don't need to.

 

[Mike.J]

A little late to the party here, but I had a similar problem to you.
I have an ASHP and an Eddi with the sensor/relay board and pt1000 in a tank pocket.
I am not sure how your Eddi is wired in, but mine is wired to control the immersion exclusively, and uses the sensor/relay input to gauge when the ashp is demanding heat from the immersion heater. I discovered that the Eddi will stop heating the water once its set temperature is reached even if the ashp is still demanding heat. So for example, if your ASHP legionella schedule is set to 60, but the Eddi is set to 50, then the water will never go over 50. Could that be your issue?

 

[Harry Bloomfield]

I did, and they said 4-5 degrees which is consistent with everything else.

DELETED - I responded to an old post..

 

[xanld]

A little late to the party here, but I had a similar problem to you.
I have an ASHP and an Eddi with the sensor/relay board and pt1000 in a tank pocket.
I am not sure how your Eddi is wired in, but mine is wired to control the immersion exclusively, and uses the sensor/relay input to gauge when the ashp is demanding heat from the immersion heater. I discovered that the Eddi will stop heating the water once its set temperature is reached even if the ashp is still demanding heat. So for example, if your ASHP legionella schedule is set to 60, but the Eddi is set to 50, then the water will never go over 50. Could that be your issue?

So in the end I've partly solved it simply by getting a new thermostat in the immersion heater. This is supposed to go up to 65, but doesn't really go above about 58. This difference could be accounted for by the difference between the pocket temperature and the actual water temperature. But I'm less worried now, particularly because @JohnD confirmed that...

> It will be killed at 50C, taking 2 hours to kill 90%. The hotter the water is the faster it dies, hence plumbers often say 60C which gives an extra margin of safety and only takes 2 minutes to kill 90%

Now my immersion has conked out completely, and I need to replace it - but that's another story!

 

[Harry Bloomfield]

This difference could be accounted for by the difference between the pocket temperature and the actual water temperature. But I'm less worried now, particularly because @JohnD confirmed that...

The pocket temperature will nearly instantly reflect the water temperature, and the thermostat will not be far behind it. Mechanical thermostats tend not to be that accurate, which is why the calibration markers are so crude looking. They also have quite wide hysteresis, often 5C difference between the on and the off clicks.