can someone pease explain this UFH system please

[ExArmy]

ok please don't take the p***, i've never wired up any central heating systems outside of a training environment, and have only done it twice!

On a job i'm doing they have just decided to go for UFH last minute, and i have been given a wiring diagram which is below and asked get the wires in for the stats so the plasterers can start this week. from looking at it i'm confused as i don't know what the clock symbol is for on the stats, i understand the L, N and SL ok, but unsure about this clock thingy, looks like it somehow links to the 4 channel time clock but if i understood it a bit more then it would make more sense

 

[snowhead]

The stats will be programable for temperature setting but not for time.
The time comes from the master timeswitch.

You need 4 core and earth to each stat position.
The stats needs L.N.E permanent to keep the display on.
Then L from the timeswitch channel which if the stat is calling is put on to the valve as SL.

 

[Richard Burns]

Agree^^^
First stat will be enabled when channel one on the time clock is "on"
Second and third stats will be enabled when Chanel two on the time clock is "on"

 

[ExArmy]

ok so i'm gonna have to second fix this UFH this week sometime. everything seems straight forward, apart from in the bottom left of the diagram it says "VOLT FREE CONNECTIONS TO THE BOILER, FOR SWITCHED LIVE CONNECT THE IN TO FUSED PERMANENT LIVE"
....and then what? doesn't go as far to say what to connect the out to, and why i would want to connect it for switched live anyway?

 

[telectrix]

witrh a volt free relay, it's just that--no connection to anything. if you want it to send a switche L anywhere, you need to apply a L to 1 terminal. if, say, you wanted it to fire a 12v relay, you would apply 12v to 1 terminal.

 

[SYKRAPS]

ok so i'm gonna have to second fix this UFH this week sometime. everything seems straight forward, apart from in the bottom left of the diagram it says "VOLT FREE CONNECTIONS TO THE BOILER, FOR SWITCHED LIVE CONNECT THE IN TO FUSED PERMANENT LIVE"
....and then what? doesn't go as far to say what to connect the out to, and why i would want to connect it for switched live anyway?

Boiler S/L if its a system boiler

and if it is a combi don't apply the PL to 'in' just remove the link across the external control terminals and connect 1 to 'in' and the other to 'out'

 

[ExArmy]

ok i think i have it, volt free connections just mean that if the boiler has volt free connections, then you just connect up to the corresponding in/out volt free connections on the boiler, but if it hasn't, connect in to fused perm live, and then out to the boiler, then from the boiler to neutral.

 

[SYKRAPS]

Don't see why you have a 4 channel clock for 2 zones though

 

[ExArmy]

ok next question,
if there are 2 zones, each with a stat (DS-SB), how many cores do i need to the 4 channel time clock? , will 4core and earth do, i'm thinking theres no point connecting channels 3 and 4 back to the wiring centre as i will only be using channels 1 and 2?

 

[ExArmy]

Don't see why you have a 4 channel clock for 2 zones though

ah you read my mind! i don't know either, it's just what turned up at the job! maybe they don't make a 2 channel one?

 

[SYKRAPS]

I would probably put the extra 2 cores in for the future, 2 x 3 core and earths rather than 2 x twin and earths, not much in it really