Caecilius wrote:
Thanks for that link: although the 0.2A capacity means it won't work
with a 2KW heater there may be similar units available that do what I
want.

I think the takeaway is solid-state switching plus low hysteresis.

If you don't mind DIYing a case, there are PID controllers, eg:

https://www.ebay.co.uk/itm/REX-C100-...t/363129928297
(they're all clones of clones of clones)

I wouldn't trust the SSR with 40A but 8A mains should be ok.

I don't know if the thermocouples would be accurate enough - quite a
difference in +/- 2C for room temperature. You might be able to manually
offset it (ie ask 20C and get 22, so ask for 18C instead).

The advantage of PID is that it should aim to keep wherever you place the
thermocouple at a constant temperature - it'll 'learn' the dynamics of the
room and the heater to avoid peaks and troughs as it overheats and then
overcools.

Theo