How to wire a wireless receiver to worcester bosch combi??

[lechat]

Hi - please help!

I have a Worcester Bosch Greenstar 25/30si. It currently has a MT10 manual timer on it but the timer dial is broken so I have to switch it on and off. I decided to replace the timer with a Heatmiser wireless programmable thermostat.

Problem is I don't know how to wire it up. The two diagrams for each product seem to say opposite things? See attached:

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• lechat
• 10 Jan 2012
• 2

Questions:

Do I have to remove the cable which currently goes from the FCU to the boiler, and run it from FCU to the receiver instead, and then put a new one on from the receiver to the boiler (as per Heatmiser diagram) or do I just leave the mains supply on the boiler and just connect the receiver to the boiler (as per boiler diagram)?

Which terminals on the boiler do I need to connect to which on the receiver? (eg on heatmiser diagram there are 2 terminals to connect, but on boiler diagram there are 3)

What cable should I connect with 0.75mms 3 core?

Also, what do I do with the existing timer that is attached to the boiler - do I need to remove it and will that break a circuit somewhere?

Many thanks in advance for your help

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[stem]

Receiver P/L (Permanent Live) corresponds to LS (Live Supply) on the boiler.

Receiver S/L (Switched Live) corresponds to LR (Live Return) on the boiler. Infact you will notice the wire is marked "switched Live"

Your boiler will still need a the mains supply from the FCU, leave it in place. The existing wiring from LS and LR should go to the broken programmer and be removed along with any other connections to it.

Then make up new connections as shown below. You will also need to take the L & N supply to the receiver from the mains supply to the boiler from the FCU.

Don't connect anything to NS (Neutral Supply) terminal at the boiler it's for older type thermostats that have an accererator heater so you don't need it.

Here's a diagram. [earths omitted from the diagram for clarity] The FCU should have a 3A fuse, so 0.75mm cable will be OK.

Untitled

• stem
• 10 Jan 2012
• 1

 

[lechat]

Hi Stem,

Many thanks for this - much appreciated.

Regarding the old programmer/timer:

The old timer doesn't connect to LR&LS, its one of those worcester bosch ones that connects to the boiler with a little plug with tiny 8 pin connector.

(http://www.worcester-bosch.co.uk/installer/boilers/boiler-controls/which-controls-go-with-my-boiler/mt10-mechanical-timer)

I'm assuming that if i just remover the old timer completely, the circuit would be broken??

There is also a "link" on the boiler between LR & LS.

So should I maybe leave the old timer in there (with its switch constantly on) and then remove the "link", and connect LR&LS terminals to the receiver as per your diagram?

 

[stem]

Sorry I don't know how the integral wiring for the mechanical timeswitch is configured. But yes you are right. Leaving it in and set to permanently "on" would work OK. You will of course need to remove the link between LR & LS when you add the wireless receiver.

You don't mention any existing room thermostat in your post, I'm assuming that because of the link between terminal LR & LS there isn't one.
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