REPLACING ROOM THERMOSTAT

Hi could anyone advise me I want to replace room thermostat with digital one and programmable thermostat.

I wish to know what amp am I looking for as they all seem to be different.

As far as I can see I have just wires going into the existing boss therm brt room stat.

Your replies would be appreciated. [/b]

I replaced our old round knob type with a Drayton Digistat 1 at around £30.00. It was a straight, easy replacement. See: http://www.discountedheating.co.uk/...L_Drayton__Invensys__Room_Thermostats_98.html

Don't waste your money on a programmable one like the Digistat 3, we thought this would be a good idea in our last house but in practice it didn't work because the temperatures in the house never seemed to behave in the way we thought they should. Also it was so damned complicated to programme that we regretted spending the extra money. Our boiler timer takes care of the times and the 'stat set at 19 in the cooler hallway keeps the rooms at a comfortable 20-21. It works perfectly and the display with the little "calling for heat" flame symbol is informative at a glance. Also being digital my wife can't nudge it up a tad when she feels cold because I notice straight away!

I'm about to move a redundant bigger rad into the hall so it will be interesting to see the effect on this setup - we may have to raise the setting to 20.

Most thermostats are compatable, although there are a few specialised ones but they are rare.

The old dial thermostats usually have three connections excluding the earth.

1) Live supply from the programmer or boiler.
2) Switched live that turns the heating components on
3) Neutral which goes to a small heater (resistor) called an accelerator
the other end of which is connected internally to the switched live so that it heats up when the thermostat calls for heat. and makes it switch off a little bit quicker.

The new electronic ones don't usually need the neutral as their electronic method of detecting the air temperature is more accurate than the mechanical version, so they just use the live and switched live. (some have batteries for program memory retention and temperature display)

Mark which wire is which before you disconnect them from the old stat, there is usually a wiring diagram inside or on the cover somewhere. If not you'll have to test the wires with a mulitmeter.

If you don't need the neutral for the new thermostat just put a screw terminal on the end to isolate it.

I'm not sure what you mean by programmable. What will be programmable? time and temperature or just temperature? If you buy a thermostat with an integral timeswitch the timeswitch you have already (assuming you have one) will need to be set to constant, or the wiring changed at the programmer. Otherwise it will still turn the system off regardless of the setting of the new one.

Hope this helps