I’ve done a lot of these in various configs at own house and clients. Here’s my general advice/experience:
- TH16 nice for temp monitoring and control - I use mostly on ring mains; found on geyser switching they tend to fail; POW R2 very reliable to switch geysers of 3kW and below - measures power consumption but not temp
- 4 ways for probe positioning:
a. stick onto flange at thermostat or (my preferred) drill small hole in plastic end cover of geyser, use screwdriver to push through insulation till feel geyser shell, continue along shell for 100mm or so, remove screwdriver and insert probe along channel created - nestling under insulation against shell is as good as inside
b. Replace existing thermostat with temp probe - not recommended when going to do switching as don’t trust TH16 to ‘fail to safe’ but if only for monitoring like in solar water or with micro probe as per @plonkster for heat pumps then okay
c. attached to hot water out pipe on top of geyser and cover with insulation
d. install dedicated probe pocket - can buy from solar water providers - bit more difficult and skills required - If have Victron install use one of Victron Pb-acid battery temp probes, take off lug, locate as per above, wire and configure to GX device and display and log on VRM - QED!! This is my solution on my 800l bulk hot water tank - have mid and top probe. If want to see how works - look here VRM Portal - Victron Energy
- starting to experiment with Shelly now but early days - looks promising though - nice and small…