Programmer Wiring

[spearos81]

I have an old Myson Apollo Fanfare 15/30 with what I'm sure is a Y plan system. Now, the programmer (which I replaced like for like a few years ago) is playing up again so I would like to replace it with something with more flexibility such as the Honeywell ST9400C.

I assume this is an easy enough job... Once you know what to connect to what!

As the existing programmer is an integral part of the boiler, as far as I know there is no 'back plate' so am I right in thinking all I would need to do is cut the wires off at the multiplug (see image) and connect to the new programmer?

 

[Blagard]

If you are thinking cutting off the 6 wires to the old programmer and reconnect them to the new one for greater flexibility then the answer is NO.

Your old programmer is wired to have HW on or CH with HW. It is not wired to allow HW off and CH on. To have independent control of HW and CH would require changes to the wiring centre.

 

[D_Hailsham]

I have an old Myson Apollo Fanfare 15/30 with what I'm sure is a Y plan system.

If you have a valve like this, probably in the airing cupboard, you have a Y Plan? What make is the valve?

View media item 5946

As the existing programmer is an integral part of the boiler, as far as I know there is no 'back plate' so am I right in thinking all I would need to do is cut the wires off at the multiplug (see image) and connect to the new programmer?

The multiplug is wired into a terminal block in the bottom right corner of the boiler. This will swing down and release when you undo the screw at the front.

Changing the wiring is a bit complicated, but not too difficult.

Hopefully the pump, motorized valve and cylinder stat are connected to a wiring centre (junction box) which then connects to the boiler.

Post what you have, pics if possible.

 

[spearos81]

Thanks for taking an interest D_Hailsham - much appreciated!

Ok, yes I have a mid position valve, in the airing cupboard. I'm 99% sure it's a Honeywell V4073.

Not the best photo - sorry!

I believe there is a junction box, also a Honeywell item. It's in the airing cupboard -

Other photos:

Any guidance about 'tweaking' the wiring to accommodate a better programmer would be great!

 

[D_Hailsham]

This is Mysons wiring for a Y Plan using the built-in timer. The wiring of the timer is not shown; it will be as in your diagram. You need to check it against your current system.

The plug for the existing timer should be disconnected at the boiler wiring strip and removed.

Apollo Y Plan

• D_Hailsham
• 10 Dec 2013
• 1

Wiring of a Y plan using the built-in timer (not shown)

This is the wiring of a Y Plan using an external programmer. The Apollo has pump overrun, so the diagram on the left need to be followed.

The link on the boiler between HW and ON must be removed and that between HW and L (if still present).

Terminal 10 in the diagram need to connect to the ON terminal (3rd from bottom) on the boiler.

View media item 31288

 

[spearos81]

Thank you.

I'll try to get my head around all of this, hopefully I won't be back with more questions but we'll see...

 

[robmorris]

Hi spearos81

How did you get on? I am in the same position with same equipment as you!

Rob

 

[spearos81]

Just trying to get my head around it robmorris!

After comparing the 2 wiring diagrams I have made the following observations:

• 
  Only one side of the junction box needs changing - the connections to the room stat, cylinder stat and 3 way valve stay the same.
  
  Only four terminals of the boiler terminal block will be used (L, N, E and ON) plus the 2 x pump overrun connections
  
  The mains connection (that was to the boiler) will go to terminals 1, 2 and 3 on the junction box on a 3amp fuse
  
  The pump will be wired to the junction box, not the boiler terminal block

Now (I think) I understand what needs to be done in theory, I need to work out what I have - if I can do the necessary changes with the wiring that is already in place, as the junction box is in the airing cupboard with the boiler in the kitchen.
So I will be looking at the existing wiring - a) does it match D_Hailsham's first diagram and b) what needs to be done to get to the second diagram.

I have a couple of questions though if anyone can help -

• 
  What does SL and PL stand for on the pump overrun diagram?
  
  I take it there would be no connection to the HTG OFF terminal on the new programmer?

 

[EFLImpudence]

What does SL and PL stand for on the pump overrun diagram?

Switched live - call to boiler
Pump live - switched on by the boiler

I take it there would be no connection to the HTG OFF terminal on the new programmer?

Correct

 

[Dezzer]

Hi,
I have been reading this post with interest as I also have this same problem.
Probably caused by the old Switchmaster programmer being replaced with a new Horstman C27.
The Boiler is an Apollo with the Pump Overrun.
Although I can follow the previously given wiring diagram can you please re-advise as to the Boiler connections.
The Boiler has an 8 wire connector block.as per the above Myson Y Plan.
Am I right in thinking that the'LIVE' wire must go from Terminal 1 of the Wiring Centre direct to the mains 'L' second from top in Boiler block.

A link from 8 to 10 in the Wiring Centre then wired direct to the 'ON' connection, 6th from top in Boiler Block.

Live from Pump, wired via Terminal 9 of Wiring Centre and then wired from Terminal 9 to Pump 'L', the bottom connection in Boiler block.

And also, NO wiring links in Boiler Block.

Hopefully this should sort things out, as at present the 3 port Mid position valve will not switch to both Heat and Water at the same time.

Thank you,