Honeywell roomstat digital replacement

I fitted a Horstmann Centaurstat in the same location. The wires merely go to a terminal strip on a thin backplate - the thermostat then clips onto the backplate. It is programmable - what is your objection?- We wouldn't be without it. - heating at the right times for work days or weekends - at the right temp for the time of day.

Can I ask why? A programmable one would be well worthwhile - but there's no real advantage in changing an ordinary one to something more modern.

I have no objection to a programmable model (other than cost and complexity); it's just that I have no need for one. The analogue one is behaving erratically and although I could simply replace it with another identical one, I like the idea of the more consistent hysteresis and temperature display of a digital model.

Incidentally, before you ask, no the problem isn't incorrect wiring or no 240V feed to the heater resistor!

Richard.

So is this a fault that's developed? Sometimes poor siting of a thermostat gets blamed on the device itself. But if it did once work correctly that's a red herring.

Right. To answer your original point most are open backed so the cable if through a wall can enter pretty well anywhere within that. If the cable is surface run there are usually knockouts for this in the usual places.

FWIW, I'm not sure the device you want exists - plain thermostats tend to be of the mechanical variety. If you want a digital readout you're halfway there to a programmable type, so that's perhaps why.

On Fri, 23 Jan 2009 10:14:14 +0000 (GMT) someone who may be "Dave Plowman (News)" wrote this:-

Horstmann DRT1.

If the Honeywell roomstat controlled the system properly before it started behaving erratically, I would just replace it with another one.

I've got one that looks identical to that, except it's marked 'TOWERSTAT RSD'. It was bought before I realised that the cable entry is near the bottom, hence my original question.

Honeywell themselves seem to do simple non-programmable digital roomstats, but as far as I can see they're only available in the States:

Richard.

No battery needed?

I'd rather have a sensor with the actual temperature controlled from elsewhere - less chance of 'fiddling'. ;-)

Indeed. If there's already a 3-wire connection with 240 VAC available, why can't digital stats use it?

Me too. The zoned UFH arrangement that we have, with independent programmers, clocks (to reset twice a year), and batteries in every room is bonkers. Does anybody make a sensible system with a central controller and remote sensors?

Richard.

The OP wanted less hysteresis

Two things - the cost and size of the power supply. Plus the mains feed may only be live with the boiler system powered up, so some types might need a backup for settings, etc.

Dunno. I remember seeing an external computer interface card with lots of isolated in/outs and software said to be flexible enough for this sort of thing. You could also daisy chain several of the cards together.

On Fri, 23 Jan 2009 05:05:12 -0800 (PST) someone who may be Richard Russell wrote this:-

Can you not cut a small grove in the wall and take the existing cable to the bottom of the new thermostat?

And plant it with ultra green trees, or olives perhaps?

Are you sure an electronic type would provide this? The older ones use a heating coil to increase this. You could simply disconnect it to reduce it.

I thought the heater *reduced* hysteresis:

I didn't actually say I wanted to reduce the hysteresis, but I would like it to be a well defined amount not determined by the vagaries of a bimetal strip and heating resistor!

Richard.

Surely the heating resistor reduces hysteresis.

In message , "Dave Plowman (News)" writes

I'm sure the digital programmable stat (Drayton Digistat of some sort IIRC, about 10 year ago?) I fitted in the old house was mains powered. because I can remember fitting an FCU in the outside cupboard to supply it

There is a mains-powered one - my last GF had one fitted when the new boiler was put in. She was a bit p'd off because I programmed it without any instructions - but I have a Drayton wireless one that's very similar.

Yes, it provides a sort of 'predictive' function, necessary because a rad. holds a lot of heat and also the mechanical system is laggy.

My 9yo Drayton electronic 'stat isn't perfect though: sometimes it'll switch on for about 5 minutes, so the boiler doesn't do a lot then about 15 mins. later it'll come on for about 10 min. The control term(s) is crude I suspect (but it has to be close to on/off for anything with a motor).