New central heating timer.

[msc0]

Hi

I am trying to replace a central heating timer and I am having some trouble working out out to wire it correctly.

My old system is wired with this diagram.

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• msc0
• 30 Sep 2012
• 1

My new system has this diagram.

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• msc0
• 30 Sep 2012
• 1

I have tried replacing what I thought was like for like but it hasn't worked.

B2 from pin 3
B1 from pin 1
A2 from pin 4
N and L transerred.

The wires I have coming to the timer are 3 multicores-

brown blue earth x 2
brown blue earth black black

the blacks were attached to 3 & 4.
L had a single brown
N had 2 blues
pin 1 had a blue
pin 2 empty

2 browns were also directly connected away from the block

I am guessing it is something to do with the fact that the new timer uses zero volt switching as opposed to switching power between 2 pins.

I have tried using a piece of wire to connect the L to A1 and B1 but can't work out what to do with the blues or even if I need to make other changes.

My system has no other thermostat.

It is a fully pumped system with a divertor by the tank to switch between CH/HW

Thanks in advance for any help I get here.[/img]

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• msc0
• 30 Sep 2012
• 1

 

[scatmanjohn]

From your description it sounds like you have a "Y Plan" (a 3 port midpostion valve)

The wiring diagram for your new timer is for an " S Plan" ( 2 x zone valves)

Look for the diagragm that refers to a mid position valve and use that.

 

[msc0]

Thanks

It seems that I do have a Y plan but no other wiring diagrams available.

Is it possible to wire up this timer as us or am I left with 2 options..

1. Return timer to supplier and look for s unplanned timer

2. Convert to s-plan. (Is this costly?)

 

[D_Hailsham]

It seems that I do have a Y plan

Your Heatmiser is not suitable for Y plan systems.