Cylinder thermostat - smart solution?

[peredelkin]

Hello fellow DIYers.
In my house I have an unvented hot water cylinder with a thermostatic pouch 1/3 of the way up. In the pouch there is a probe attached to a thermostat that controls a valve on the primary circuit, whose dry contact is connected to the call for heat from my boiler. So far so good.
What I don't like about this setup is that it is a bit dumb. For starters, the thermostat is a cheapo piece of plastic and very imprecise in its measurements. Secondly, I have no visibility over the internal temperature of the cylinder.
Is there any way to make this smarter?
I was thinking I could potentially replace this dumb plastic thermostat with a ds18b20 temperature probe, and use that as a temperature input to a smart device that controls the valve. Would something like that work? Is there a product that has the appropriate 1/2" thread to screw onto the pouch?
Any other ideas to improve on this?

 

[oldbuffer]

1. Its an unvented hot water cylinder. By law, no one is allowed to work on them without a current accreditation to a G3 scheme.
2. The thermostat is part of the multi-level safety system which applies to these cylinders.

 

[peredelkin]

1. Its an unvented hot water cylinder. By law, no one is allowed to work on them without a current accreditation to a G3 scheme.
2. The thermostat is part of the multi-level safety system which applies to these cylinders.

I am fully aware of the security features of unvented cylinders, and I am not planning to carelessly open up the cylinder and compromise its safety features for the sake of DIY. Plumbers are not always up to date with smart controls, and often times are allergic to anything that isn't similar to what they have been doing for the last 20 years, that's why I asked if there is any appropriate product for my setup, and I am planning to run this through my plumber at the next annual inspection in case there is any doubt about its safety.

Besides, since you brought this up, let me say one thing about so-called "accreditation schemes": they are a fraud, and they are certainly not there for your protection or mine. I have seen too many instances in which "accredited" people just put their stamps of approval on horrid setups that were of dubious safety, if not outright dangerous.
Take this very cylinder: it is fitted with both a primary circuit coming from the boiler and a separate electric immersion heater, which is connected to a switched fused spur that I can turn on manually in case of boiler failure. The stat is connected to the boiler controls, so when temperature is reached it'll stop heating. Yet, the original installer did not connect the stat to the electric immersion heater, which I suspect means if I turn it on and forget to turn it off it could lead to the cylinder going kaboom*. And yet, this cylinder passed not one but two annual gas safe inspections with flying colours.
Or shall I mention my fuse box being in close proximity of my gas meter without the appropriate fireproof partition, which passed both the gas and electrical inspections?

* = Yes, yes, I know that there is also the pressure release valve above the tundish.

 

[muggles]

EPH CP4-HW-OT. Paired with a CP4i you get a very reasonably priced setup with a nice user friendly app

 

[fixitflav]

Yet, the original installer did not connect the stat to the electric immersion heater

An immersion heater usually has a thermostat built-in.

 

[Madrab]

Plumbers are not always up to date with smart controls

It's not the plumber that dictate safety measures, rather the manufacturer, in conjunction with regulator. They test and approve what those safety systems are and how they are implemented through testing and certification. The engineer is not allowed to just take it upon themselves to design their own approaches to those safety devices. That's as much for their safety as well as the clients.

With unvented cylinders there is usually a built in cylinder stat that lives in a pocket and is part of the control/ high limit stat setup, connected to a safety cutoff (2 port). Could another 'smart' control be added to provide more accurate temperature control, yes, but the supplied HL/Control safety systems wouldn't be removed nor would the new smart control be allowed to override the pre-installed safety systems.

The immersion heater wouldn't be wired into the cylinder/HL stat, it has it's own internal stat for cutoff and if that fails then it failsafe's to the TPRV/PRV.

 

[peredelkin]

It's not the plumber that dictate safety measures, rather the manufacturer, in conjunction with regulator. They test and approve what those safety systems are and how they are implemented through testing and certification. The engineer is not allowed to just take it upon themselves to design their own approaches to those safety devices. That's as much for their safety as well as the clients.

With unvented cylinders there is usually a built in cylinder stat that lives in a pocket and is part of the control/ high limit stat setup, connected to a safety cutoff (2 port). Could another 'smart' control be added to provide more accurate temperature control, yes, but the supplied HL/Control safety systems wouldn't be removed nor would the new smart control be allowed to override the pre-installed safety systems.

Just a follow up: you are right, and the guy who came to do the annual maintenance confirmed that while there might be better solutions out there, if the manufacturer of the cylinder hasn't specifically approved a solution then the cylinder will fail the annual inspection.

So, soz, I will be stuck with the crappy thermostat.