Hmm now I'm wondering about this...

http://www.ebay.co.uk/itm/Thermostat-Te ... 1147036059

A PID will work, but the beauty of Caravels is that you should be able to use them as is. When you took it apart did the rocker connected to the microswitch move freely or is it somehow a bit creaky? Are the rocker pivots at all rusted or corroded? Is it well fastened down?

I didn't see any cause for concern on any of those fronts. It turns on and off, just too wide a deadband.

Meanwhile, I've had the boiler pop out a few times, so I've ended up bending the retaining bit at the top of the main body. Seems to be working a bit better now, but will be a few days before I'm sure I'm out of the woods.

wintoid wrote:It turns on and off, just too wide a deadband.

I was referring to the wide deadband and hope you can resolve that. I'm also wondering what causes the wider deadband because the thermostatic mechanism is so simple that it would have to be a mechanical issue, not an electrical one.