Every other email from Screwfix tries to sell me a Nest or Hive system, so I thought I'd have another look at them with my holiday flat in mind.
I currently have an S-Plan system with an unvented HW cylinder. There is an electronic (manual) timer for both HW and CH. The HW circuit has a tank stat which controls the HW 2-port valve. The CH heating valve (both timing and temperature) is controlled by a wireless programmable thermostat (with the CH side of the manual timer being set to permanently on). There are TRVs on most radiators.
The current system provides *most* of what I need, but it doesn't allow the heating to be switched on and off remotely not does it allow the temperature to be monitored remotely. The flat gets pretty cold when unoccupied in the winter months and it would be nice to be able to turn the heating on a few hours before we plan to arrive each time so that it's warm when we get there. In theory we could do this by using the 'holiday' mode on the programmable stat, but that requires us to know when our next visit will be - and we don't always know that.
I'm not interested in a system which is too clever by half by trying to second guess when we're in or out nor in anything with any more zonal granularity than a single heating zone with a few TRVs. On that basis, a Hive 2 system appears to be a pretty good match. Although there's no real need to have remote control of the HW, this is included with most of the Hive 2's on offer, so I may as well use it - and get get rid of all the current timing devices.
I've read past threads on the subject and the Hive 2 Installation Manual, and I have a few queries to which I haven't been able to find answers.
How does it do HW control? There's no mention of a HW temperature sensor so I assume that it is used in conjunction with the existing cylinder stat, and just provides timing. Is that correct? What does HW boost do? I assume that it simply turns the HW circuit on at a time when it would otherwise be off - leaving the cylinder stat to control the temperature. Is that correct?
What does CH boost do?
It appears that the heating can be remotely controlled by SMS messages for the benefit of people who have tradition mobile phones rather than smartphones. How does that work? Is there a SIM card in the unit, or does the SMS message go to a Hive server which then communicates with the unit over the internet? If the former, do you have to pay for a mobile service of some sort?
Some people have expressed concerns about being reliant on an external server - which could be withdrawn at any time. Since Hive is a British Gas system, I doubt that BG will cease to exist any time soon, but have they made any public pronouncements about long-term support for Hive? AIUI, once you have bought the hardware you can access the Hive servers for free without having to pay any subscription charges (unlike trueCall junk call blockers, for example). Is this correct?
Answers to the above questions from those knowledgeable in the subject will be much appreciated.