central heating controls wiring

[sarmavsn]

Dear All, I had a Honeywell room thermostat which controlled the Alpha Combi boiler in the loft. I tried to replace it with a Drayton Digistat 3. It did not work. Can any one please expalin what is the meaning of the terms, call for heat, satisfied etc? What do thes wires do in real terms? When I put an ohm meter across the three terminals of the digistat, nothing happens as the programme calls for heat. Does this work by connecting terminal 1 to 3 or does it send a voltage signal? Can some please explain how the system works? thanks sam

[Peter Andrews]

should allow you to work out your problem.

Peter

[Dave Plowman (News)]

IIRC, these are available in both battery and mains versions. Which one have you?

If you imagine a switch with an input but two outputs one of which is live and the other dead when the switch is 'off' and reverses when it is 'on'. That's what most thermostats have with the 'switch' operated by the thermostat.

With the thermostat set to higher than ambient temperature one output becomes live and this is the call for heat sometimes marked 'on'. When the room temperature exceeds that of the thermostat the switch changes over and the call for heat becomes dead while the other (satisfied) output (can be marked off) becomes live.

The top terminal is the common so has the live feed. Next down is the on, and the third off.

[John]

I think the best option would be to put your new Drayton Digistat 3 on Ebay or get a refund and get one of these

which is specifically designed for Alpha boilers. I've got one and it's absolutely brilliant.

J.

[Dave Plowman (News)]

The one it's replacing doesn't seem to have been a 'special'. What's so different about Alpha boilers?

[John]

The thermostat is a changeover switch. The live feed is switched to "Call for heat" when the room is below temp and to "Satisfied" when it hits the temp. Therefore the call for heat needs to be connected to the pump / boiler .

[John]

Don't know if you actually clicked on the link Dave but it links to a page on the Alpha website detailing the 7-day Wireless Digital Easy-Stat. The clever part is that, being designed specifically for Alpha boilers the receiver part of it just mounts in the boiler itself in an existing hole, replacing the existing timer options one-for-one, utilising the same spade connections. The transmitter can be mounted anywhere (but the OP will, presumably, want it in the same place as his existing programmer). The whole thing can be fitted, programmed and working within 5 minutes - and it can be retro-fitted into existing Alpha boilers.

John. PS, never sure about netiquette - should I be snipping out your (anyone's) sig when I reply? It's not so bad on a single reply but it can take up loads of room when it gets to 5 or 6 postings in a thread :o)

[Dave Plowman (News)]

The Drayton Digistat 3 is also a changeover type. So if the system worked fine with the original Honeywell it will too with the Digistat.

[Dave Plowman (News)]

I did, but it's one of those websites that don't load properly on this browser so I lost interest.

Handy for a new fit, I'd say, but the OP just wants to replace an existing stat with a different one, so the wiring must already be in place.

Yes, you should remove it. Better newsreaders will do it automatically as that's the purpose of the sig separator. (-- )

[Roger Mills]

A decent newsreader will do it for you - or even an indecent one with the right plugins!

I use a thing called "OE-Quotefix" in conjunction with Outlook Express. It automatically removes signatures, and leaves the cursor at the *bottom* - just ready for typing your reply without any danger of top posting.

Quotefix is a free program (Google for downloading details) which attaches itself to OE, and needs very little setting up - although it does have setup options which you can use if you like.