Digital Thermostat Wiring

[MHR43]

I want to replace a defunct (dial type) room thermostat with a basic digital thermostat.
The mains supply to the thermostat is a 2 core, brown and blue cable.
The terminals on the old thermostat are not marked. The new thermostat terminals are marked-
1. Com
2. NC
3. NO

Which of these terminals do I connect the blue and brown wires to?

 

[CBW]

I don’t think that set-up will work, as you have no switching wire. You would need 3 core cable for that. There are 2 core wireless stats and 2 core digital stats available but you’d need to research which one and form which boiler.

 

[muggles]

Normally you'd use terminals 1 & 3 on the new thermostat, but you need to check whether your blue wire is a switch Live, or a Neutral

 

[ianmcd]

The existing 2 cores go between 1&3 on the new thermostat, doesnt matter which way around it is just a switch

 

[ericmark]

The NO means normally open and the NC means normally closed, so we would normally use the NO as then when battery becomes discharged the thermostat will switch off, some thermostats have a little switch to swap if normal is high or low temperature so it can be used for air conditioning or heating, but in the main we use only the NO contact and common.

I assume your talking about the display when you say digital? And both are digital thermostats, i.e. switch on/off. Analogue thermostats are far better, they reduce the hysteresis and save on fuel, but they are wired completely different, they connect to the ebus of the boiler reducing or increasing flame height rather than simple on/off.

The digital thermostat still has a place with modern central heating, it stops cycling once the lower limit has been reached in the output of the boiler, but there is a problem controlling room temperature, the TRV controls the room temperature the wall thermostat controls boiler not room.