Cylinder thermostat voltage

[alchemist]

Hi,

Rewiring to a honeywell L641A1005 cylender thermostat and confused by the voltage readings there.

It's suppled by a Three core and earth in old colours. Red connected to brown on the flex, blue to blue and yellow to earth (although the yellow is not earth so I suspect the installed just used the earth wire on the flex - naughty I know).

Does this wiring sound correct, and what voltage should I get on each wire.

I'm getting 50v on yellow and I think 240 on red. I'm assuming that blue is switched live and yellow I have no idea. Should yellow be 50v, is it be a control wire of some sort? I'm going back to look at why they now have no hot water since I did the rewiring and want to be sure i'm wiring correctly.

 

[PC Electrics]

The 50v on yellow is probably the backvoltage from the valve (assuming it's a Y plan - which you haven't specified).

Go to the Honeywell site, register for the downloads section and there you will find all the plans and a large document (somethingorother_issue14 Ithink it's called) which includes a ection on electrical check out of all the plans.

Can't link to it directly because if you're not registered you can't get into it, so you'll have to find it for yourself.

The tank stat should be using a 4 core (I use 5 core flex 'cos that's what I carry) - using a g/y core as a live is a no no in the regs.

Heat Resistant - Buy quality Heat Resistant at Screwfix.com

 

[Sidewinder]

PC,

I think the OP has RYB three core flex int he old phase colours rather than that with a G/Y core in which case Y as a live is OK as it was one of the old phase colours.

I have not really thought about this post much, but something does not seem quite right, your suggestion of the Honewell book is good.

Until I came on here I had never heard of the terms S plan, Y plan etc.!

I have always just wired them up my way to make them work the way the customer wants, after all it is just switches and actuators basically!

 

[Doc Hudson]

To know what voltages you are likely to expect, you will need to know what sort of heating system is it, S-plan, Y-plan etc, and if it has two port valves or a mid position 3-port valve? As a general rule colours mean very little on central heating wiring as there is no standard.

Doc H.

 

[Sidewinder]

Certainly aint if I wired it Doc!

Only thing I NEVER do is use G/Y as anything other then earth/cpc.

 

[alchemist]

Thanks for your advice guys. In the end it turned out the customer had no hot water because the thermostat was faulty - my colleague broke it doing IR tests I think. A spark I know also said 50v might be back-feed from the valve. I'm going to check out the Honeywell site, sounds really useful. I too had never heard of the different plans.