Not knowing the data of the new combi boiler, I am in the process of wiring the themostat should i use twin and earth or 3 core and earth?

I would use 3+e in case the stat needs a neutral!

Although it will work with just L and S/L, if you don't have a neutral then there is no voltage placed across the resistor when the switch operates.

The resistor prevents the room temperature swinging too far past the selected temperature by creating a tiny amount of heat within the thermostat. This counteracts the delay in the thermostat sensing the actual room temperature. So best to go for 3 core: L S/L & N if you have the opportunity.

depends on the boiler, most models commonly rely on a current being passed through to the S/L connection. Its normally fitted with a wire link between two terminal blocks. I usually run a 1.5 T+E. However, like others have suggested, check the boiler manual incase it requires a Neutral. New Glowworm, Baxi models have the 2 wire system.

3core, and dont cut off the unused cores.

Remember combi boiler will last 15years and your cable will outlast boiler so next boiler might require a neutral at the stat even if current boiler doesnt

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Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!

I always install 3 core+E

MInd you, came across an underfloor heating package the other day that needed 4 Core for the stats!

Dont assume - check

For crying out loud.

In a normal domestic situation I really wonder who actually would notice or be bothered with the difference between a stat with neautral and a stat without.

If it's too cold you turn the stat up, if it's too hot you turn it down.

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S George
http://www.state-it.com

Probably just the die hard eco warriors because where a neutral is required, but not connected, the boiler runs a tad longer than necessary to reach the selected temperature.

My other half did... (she seems to be able to sense 0.5 degree errors, especially when below the setting)

- Andy.