Tank thermostat for vented cylinder

[Xerxes991]

My ancient clamp-on cylinder stat needs replacing. I would like one that allows me to read the current tank temperature as well as set the target temperature. Ideally, it would let me do that via smartphone app, but a local display would be ok. 
That should all be easy in 2022, you would think. But I’m struggling to find any, other than ones designed to fit in the pocket of an unvented cylinder. 
Any suggestions, please? 
Thanks, Steve W

[PeterW]

Drayton Digistat+C RF will do that for you - just not the phone / app bit

[Radian]

 

52 minutes ago, Xerxes991 said:

Any suggestions, please? 

How handy are you with a soldering iron? 

[Xerxes991]

9 hours ago, Xerxes991 said:

My ancient clamp-on cylinder stat needs replacing. I would like one that allows me to read the current tank temperature as well as set the target temperature. Ideally, it would let me do that via smartphone app, but a local display would be ok. 
That should all be easy in 2022, you would think. But I’m struggling to find any, other than ones designed to fit in the pocket of an unvented cylinder. 
Any suggestions, please? 
Thanks, Steve W

 

9 hours ago, PeterW said:

Drayton Digistat+C RF will do that for you - just not the phone / app bit

Thanks Peter. I was hoping to spend rather less than that 😟. I don’t need the RF functionality since the TS wiring is already at the cylinder, and I can add a permanent live feed fairly easily. So I was hoping for a “simple” switch with local digital readout. 
 

[Xerxes991]

9 hours ago, Radian said:

 

How handy are you with a soldering iron? 

Not bad (for a mechanical engineer). Have you got a home brew suggestion? Sounds interesting. 

[Radian]

58 minutes ago, Xerxes991 said:

Not bad (for a mechanical engineer). Have you got a home brew suggestion? Sounds interesting. 

 

Well yes, there's a thousand ways to implement such a thing - it all depends how much from first-principles you are happy to start with. Assuming you'd rather not create your own temperature sensor from a forward biased diode I'd suggest using a ready made temperature sensor like a DS18B20. Then you grab a raspberry pi and follow steps from any online tutorial like this one to hook it all up. That link has a video tutorial as well.

 

 

If you were to follow it you'd end up with the temperature on a display. The Python code example could then be tweaked to operate a 240V relay board to produce a boiler demand contact closure at your chosen set-point. A relay board like this for example...

 

 

...Can plug straight on to the Raspberry Pi pins. You could put probably it all together for under £50. Once you have the basics working there are numerous ways to go about making it smarter should you wish to. 

[Xerxes991]

That’s amazing. And I do have a Raspberry Pi, but I think my airing cupboard might not be the best place for a project like that. 
I’m leaning towards the ESI device, which is designed for unvented cylinder with pockets. But I’m sure I could just embed the sensors, in contact with my cylinder wall. Does that sound reasonable?

 

ESI - Energy Saving Innovation Controls ESCTDEB ESI Controls Electronic Dual Cylinder Thermostat, White https://amzn.eu/d/5YI7znx

[Radian]

That wouldn't work on my system as I have the flow temperature set to 60^oC to keep the boiler in condensing mode and it has only the one flow temperature so once a week it would stay on 'forever' while attempting to complete their Legionella program.

[Xerxes991]

9 hours ago, Radian said:

 

That wouldn't work on my system as I have the flow temperature set to 60^oC to keep the boiler in condensing mode and it has only the one flow temperature so once a week it would stay on 'forever' while attempting to complete their Legionella program.

 

Good point. I would plan only to use it as a simple thermostat, with all the ON/OFF cycles set in my new Hive thermostat. So I could set the Legionella cycle to be time constrained within one of the ON periods, when all other zones are off. 
Any suggestion on how to ensure best thermal contact between the sensors and the copper surface of the cylinder?

[Radian]

47 minutes ago, Xerxes991 said:

Good point. I would plan only to use it as a simple thermostat, with all the ON/OFF cycles set in my new Hive thermostat. So I could set the Legionella cycle to be time constrained within one of the ON periods, when all other zones are off. 
Any suggestion on how to ensure best thermal contact between the sensors and the copper surface of the cylinder?

 

Are you sure that's possible? the manual I found makes it sound like it's automatic:

 

"Boiler Setting To ensure the elimination of Legionella Bacteria in the Hot Water Cylinder, at least once a week the Cylinder should be heated to 61°C. This is carried out automatically by the ESCTDEB. The Boiler Thermostat (output temperature) must therefore be set to maximum and homeowners 9 should be made aware that once a week the hot water will be warmer following the automatic “weekly boost”. We also therefore strongly recommend the use of a thermostatic mixing valve (TMV), these blend hot water with cold water to ensure constant safe shower and bath outlet temperatures, preventing scalding."

 

[billt]

I have the ESI thermostat on an unvented cylinder (although I did specify pockets in it) and it works fine. You can disable the anti legionella cycle, which I have done. I run it at about 47C.

 

The cylinder is quite small and the flow rate has been adjusted so that, even with a flow temp of 70C, the return temperature doesn't get above 45C, so the boiler should still be condensing. It only takes 20 minutes to heat the cylinder form cold so it doesn't matter too much.

 

My only issue is that the hysteresis is too small, so the boiler fires even if you've only drawn off a fairly small amount of water.

[Xerxes991]

14 minutes ago, Radian said:

Are you sure that's possible? the manual I found makes it sound like it's automatic:

Thanks for the manual link. It’s not clear what happens if it does not achieve 60 for the full hour. Does it simply stay on demand at that temp until the condition is met, I wonder?
The manual also goes on to say the timing/frequency of the “boost” can be adjusted, or totally disabled. If necessary I could manage without the boost perhaps. I’ve survived without Legionella protection for 70 years so it’s probably one of my less important health risks! 
The device is £25 and seems a bargain. I’ll call their tech people (?) and see if they do a version for vented cylinder, and what they suggest about attaching the sensors. 
Many thanks for your comments - much appreciated. 

[Xerxes991]

Thanks Billt 

That’s very helpful. My conventional (therefore quite large) vented cylinder is reheated periodically, rather than on demand, so the small hysteresis is not a problem for me. 
I think I’ll give it a go. Just have to make sure the sensors are in intimate contact with the copper wall, and well buried in insulation. 
Steve W