Tank thermostat very inaccurate

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I have been buying cheapish Hot water cylinder thermostats in the past but have had to change a couple recently as they just packed up!
So I bought a Honeywell stat but that was so inaccurate I sent it back.
Bought another one and it's the same.
I have probes that i have calibrated with freezing water and boiling water so I am fairly certain that they are accurate.
What happens is even with the tank stat set to 80c it's turning off at about 45c !
is there a way to adjust these or am I going to have to try another make.
If so what would you recommend ?
Drayton?

thanks
Mike
 
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I have been buying cheapish Hot water cylinder thermostats in the past but have had to change a couple recently as they just packed up!
So I bought a Honeywell stat but that was so inaccurate I sent it back.
Bought another one and it's the same.
I have probes that i have calibrated with freezing water and boiling water so I am fairly certain that they are accurate.
What happens is even with the tank stat set to 80c it's turning off at about 45c !
is there a way to adjust these or am I going to have to try another make.
If so what would you recommend ?
Drayton?

thanks
Mike
If at a certain setting it gives you the HW temperature you want, and it has a reasonable differential, so not starting/stopping the boiler too often, does it matter what the markings say?
 
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I have probes that i have calibrated with freezing water and boiling water so I am fairly certain that they are accurate.
What happens is even with the tank stat set to 80c it's turning off at about 45c !

The temperature, depends very much on where you measure it and the stat itself will allow for this, so your measurement technique might be the cause of the error. You should have no need to set it to 80C, in fact most boilers (is it a boiler?) will not be able to heat water to that temperature anyway. 60C is the more usual setting, to ensure there is no Legionella in the hot water system. Hysteresis is the essential difference in temperature, between on and off, to limit frequent switching on and off, usually around 5C difference.
 
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Thanks for replies.
It is for a solar heated tank that can go up to 90c the stat is at the bottom 3rd of tank and according to my readings the stat should turn off at about 60c to give 80c at the top roughly.
but its turning off at about 40-45c so a lot of free energy is being wasted.
So the stat set at 80c is operating at 45c max ! that's not really acceptable for this situation.

I've used
Flomasta 03 26 270SX before and they do at least work. But they seem to go wrong after a few months!

Thanks
 

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