On Sun, 30 Dec 2018 09:59:01 +0000, David wrote:

As discussed previously I suspect I have a fault in the 3 port valve.
Drayton Mid Position Actuator MA1.

For diagnostics, do I have to do more that check that when CH is called
for by the programmer power goes to the thermostat, and when the
thermostat clicks on power comes back to the valve?

I am assuming that the sequence at the valve is:

(1) CH request from the thermostat

(2) Mid port valve moves to open CH port

(3) Controller then calls for pump and boiler

This has the second assumption that if (2) fails to happen then (3) will
not happen (which seems to be more or less what is happening).

Diagnostics day tomorrow, hopefully.

O.K.
Further help required, please.

First a view of the wiring in the wiring box.
http://wiki.diyfaq.org.uk/index.php/File:Central_Heating_wiring.JPG

Next a view of the wiring instructions inside the lid.
http://wiki.diyfaq.org.uk/index.php/File:CH_wiring_diagram.jpg

Finally the wiring diagram from Drayton.
https://www.draytoncontrols.co.uk/sites/default/files/IG.%2022mm_0.pdf

When the power is on, the programmer has CH turned on and the thermostat
is calling for heat then there should be current flowing to/from the white
wire in the PDF.

Looking at the PDF it seems as though the common terminal is live and the
calling terminal is neutral. I assume with 240V AC this is largely
irrelevant for basic diagnostic purposes.

So for testing purposes, working from the table inside the lid of the
wiring loom, there should be power between COM and CALL (2 and 3) and 2
should be linked to 4 which should then pass power to the white wire from
the Mid Port Switch.

Or is it?

This is where I get horribly confused because in my first round of testing
it seems that if I have power and the programmer calling for CH but the
thermostat turned right down, I get 240V between 2 & 3 and 2 & 4.
If I have the same with the thermostat turned right up then I get 0V
between 3 and both 2 & 4.

This is the opposite of what I was expecting.

Regardless, with 240V or no 240V between 3&4 the pump doesn't run and the
boiler doesn't fire.

However to proceed with the diagnostics I need to know that my first step
is correct.

I think my next step will be to take the thermostat off the wall and check
the wiring there. There should (according to the PDF) be live and neutral
into the thermostat (but why?) and a third wire to carry the call for heat.

This does seem to be reasonable, because if the programmer is calling for
heat then you can hear the thermostat click on and off, but if the
programmer isn't calling for CH the thermostat doesn't click.

Any advice most welcome.

I keep adding to this. Would a valid test be to disconnect the white wire
from 4 so that I'm only testing the thermostat output assuming 3/COM is
the live feed?


Cheers


Dave R

--
Dell XPS laptop running W8.1