room thermostat

[jjb1333]

Hi
I want to renew my old fashioned looking room thermostat
I have bought a nice slim line modern one and notice that when taking off the old one i have two red wires and one black and an earth
The new one says on the box simple 2 wire installation

Can any one tell me how i wire up the new one ?

Many thanx

 

[45yearsagasman]

Model of old and new stats would help!

 

[Steve]

Probably use the two reds as the "2 wires". The old one would have had a neutral.

But await confirmation. Was the old one JUST a stat?

 

[jjb1333]

The old one was a honeywell,i dont know what model but its really old
The new one is a Salus
Its just a basic manual one not digital
Thanx.

 

[Taylortwocities]

They will all have model numbers on them. That is the only way to be certain , guesswork may blow the new stat/heating programmer etc.

The model number of each will be on the back or front of the stats.

otherwise.......

Untitled

• Taylortwocities
• 17 Nov 2009
• 25

 

[mfarrow]

The old thermostat had a little heater inside it (heat advance? I think the feature's called). Basically it gives better accuracy for temperature control. It needs the neutral (black) for the heater.

The new one doesn't have this feature, so may not be as accurate in service as the one you're about to throw away. In which case it should be the two red wires you need.

Make sure the old black cable is either terminated in a crimp or terminal block, or both ends earthed and identified as such.

 

[ajrobb]

The old thermostat had a little heater inside it (heat advance? I think the feature's called). Basically it gives better accuracy for temperature control. It needs the neutral (black) for the heater.

The new one doesn't have this feature, so may not be as accurate in service as the one you're about to throw away.

The old heater resistor was an option for small loads. If you use a heavy load (like an electric fire), the resistance of the thermostat would heat up the bi-metal strip. For light loads (typical central heating), the heating resistor could be wired in to heat up the bi-metal strip. Heating the bi-metal strip when on reduces hysteresis (the difference between on and off temperatures).

With the new thermostat, you can judge the hysteresis by turning up the temperature control until it turns on and turning it back down until it turns off. The difference in the two temperature settings indicates how much the house will heat up between the heating coming on and going off. This difference may be quite noticeable and you could end up with a higher setting for comfort than your old thermostat permitted. In turn, this will lead to higher fuel bills (maybe 5% for the same comfort).

FYI other models were similar but had a lower resistance (more heat) for 'back off'. This could use a simple timer to lower the set point rather than turning the heating off completely.