Y plan wiring

[IJWS15]

Puzzled

fitting a hive thermostat and all seems to be working so opened the wiring centre to link out the old thermostat and found this

apart from the terminal numbering not matching the faded numbers where should the loose blue wire be connected? It is from the tank stat.

If I can find a diagram I may start from scratch with correctly numbered terminals.

is it a problem if the tank stat earth isn’t connected? It doesn’t appear to be!

 

[IJWS15]

Looking again there is a loose black wire as well…… also from the tank stat.

Only one wire was connected to the tank stat (common to T6 not that it means much) no one has touched it since the guy who serviced the boiler changed the three position valve actuator a year or so ago so the wires have bee loose at least that long.

tried common to T6 and the other two to T7 and T8 then vice versa and neither move the valve to heating.
looking at the tank stat case is cracked SoI need to get one.

 

[terryplumb]

There are plenty of Y plan wiring diagrams on the internet ,and YouTube videos too.

 

[Johntheo5]

This one may help.

 

[Exedon]

Honeywell have a really good app you can download.
Look for Honeywell home wireing guide all the different plans Y - S - W - C are all there.
It includes a troubleshooting section.

 

[Hugh Jaleak]

Have a look here: http://octaveblue.co.uk/central_heating.html

Earth wires, I would connect them up as a matter of course, and remove any possibility of a stray wire touching a live terminal, and possibly making the entire heating system live! (Check no-one has used an earth as a conductor though first! Shouldn't do, but you never know.....)

 

[IJWS15]

Thanks for the suggestions, I found the diagram in the boiler instructions and followed that, working now but no idea how it worked yesterday.

One addition is a neutral wire from the wiring centre down to the boiler . . . I couldn’t see where else the pump/boiler stat would get neutral! Luckily when they installed it they ran a triple and earth from the boiler to the wiring centre. There is no LNE feed from the dp switch, just the switching feeds from the controller, I have a feeling there is an LNE feed to the boiler from somewhere as there are connections near the boiler but no idea where they come from.

 

[ericmark]

My daughters first house had Y plan, what a nightmare, in the main due to lack of information.

the internal wiring diagram seems hard to find, surprised allowed today, the internal diodes and resistors means one can get some very odd readings, and one needs a type A not type AC RCD with this arrangement as that diode can freeze some RCD's and stop them working. It needs this

on the RCD, not just the wavy line.

The problem with daughters was one of the V3 micro switches was stuck in, this had been got around by latching the bleed leaver on, this resulted in central heating running when it should have only been heating hot water, it was a Sunday, so could not get a micro switch, had to swap whole valve.

The main reason for Y plan is the boiler had no cooling down time, and the Y plan default is domestic hot water, so boiler can cool by heating the domestic hot water, even if only with thermo syphon.

It is clearly better than the C plan which I have with this house, which also allows boiler to cool by heating the DHW.

Today most seem to use the W plan, and it is built into the boiler.

I have noted some manufacturers of boiler stipulate type A RCD's, but today we are not permitted to fit type AC anyway, but we were late adopting that requirement.

 

[Johntheo5]

Y plan is very ingenious IMO, it even uses DC braking to hold the valve in mid position but is also quite cunning because of its "last port of call" design, even if you have programmeed the DHW+CH on there is no guarantee that it will default to the HW position when both systems are programmed off, say at night. If you switch off both CH & HW and then switch on the HW only then the valve will only spring return to the HW position if the cylinder stat is calling for heating, the CH position will still cool the boiler Hx down if pump overrun is fitted. The motor may not last as long as a 2 port because of this as it will more than likely be running every night in winter with CH its last port of call.