On 31/12/2018 16:17, David wrote:
On Mon, 31 Dec 2018 15:55:26 +0000, David wrote:

snip

Addendum:
http://wiki.diyfaq.org.uk/index.php/File:Wiring_Links.jpg
Links on the back of the wiring block.

Looks to be a link between 3 and 9 which is puzzling me.

Cheers


Dave R



Can you remind us whether this has *ever* worked properly. If it hasn't,
it's most likely that it's wired incorrectly. If it *has*, it has
presumably developed a fault - most likely associated with the 3-port valve.

The only wiring diagram you should need is this one:
http://wiki.diyfaq.org.uk/index.php?...lan-Wiring.gif

Clearly your connection box doesn't use the same numbered terminals for
the same things, so you will need to work out the equivalence. In order
to design any diagnostics, it's important to understand how a Y-Plan
system works and, in particular, the part played by the 3-port valve.

There are two electrical inputs to the valve actuator - white (heating
demand) and grey (hot water off or satisfied) - and one output (orange -
switched on by the valve in the heating-only state).

When there is a HW demand but no CH demand, the valve is unpowered and
its spring return holds it in the HW position. The boiler (and pump if
the two are connected together as shown)[1] is powered from (1) on the
cylinder stat. The white and grey wires will be at 0v but the orange
wire will be at 240v even though it's not being switched by the valve,
because it's connected to the boiler.

If you now add a CH demand, the white wire will be at 240v, and will
cause the valve to motor to the mid position. The boiler and pump will
still be powered from (1) on the cylinder stat.

If you now remove the HW demand, so that there is only a CH demand, the
grey wire will go to 240v. [This assumes that there is a HW-off
connection on the programmer and that the cylinder stat has change-over
contacts, as shown - without which the system won't work]. This causes
the valve to motor to the CH position, at which point a micro-switch is
operated which switches live from white or grey (can't remember which)
to orange. The boiler is no longer powered from (1) on the cylinder stat
but is powered by the orange wire instead. Clearly, if that micro-switch
doesn't do its job, there will be no power to the boiler and pump.

Y-Plan systems can be difficult to diagnose because connections which
you don't expect to be live often are because they're connected to
something else which is live (e.g. the orange wire) or through induction
or the internal workings of the valve actuator.

I've known actuators simply getting 'confused' - requiring the system to
be completely powered down, after which they work ok again - but I guess
you've tried that.

I had lots of problems with my system when it was configured as a
Y-Plan. In the end, I bit the bullet and converted it to S-Plan -
replacing the 3-port valve with two 2-port valves - and have never
looked back.

[1] If your system requires pump over-run, the pump may be connected to
dedicated terminals on the boiler, and not simply wired in parallel with it.
--
Cheers,
Roger
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