Help with wiring centre

[NORDENHEATING]

I am looking for a little help with a wiring centre and the wiring formation for a system boiler. I have no problem wiring a conventional system with external pump and 3 port valve, but the fact that the pump is internal is tending to concern me, due to the feed being from the boiler. What happens to the pump terminals in the wiring centre ?. The live feed to the boiler, no problem, the live out and switched live to and from the wiring centre respectively, but which terminals ? The boiler by the way is a Baxi Megaflo system boiler.

Thanks in advance

 

[D_Hailsham]

due to the feed being from the boiler.

Do you mean the electrical feed to the boiler or to the pump?

The pump is incorporated in the boiler and wired internally, so you just ignore the pump connections in your wiring centre, just provide the switched live [usually terminal 8] from WC to boiler.

Ideally the power to the wiring centre should come from the boiler. This ensures that turning off the power to the boiler also turns it off to the wiring centre, motorized valves etc.

The live feed to the boiler, no problem, the live out and switched live to and from the wiring centre respectively, but which terminals ?

Is your timer built into the boiler or external, connected to the wiring centre?

 

[doitall]

All external wiring is to/from 1 & 2 in the boiler, after you remove the link, and must be suitable for 240v switching.

 

[NORDENHEATING]

Hi

Thanks for the 2 replies. I understand the permanent live feed from the fused spur goes to the boiler, the feed to the wiring centre comes from terminal 1 at the boiler to ( I assume) the live supply terminal in the wc. The time clock is external as the megaflo does not have an integral 2 channel clock. This would be wired into the wc. The bit that I can't get my head around is where does the switched live come back to the boiler from (position 2 on the boiler), is it the live that should go to the pump ?
as this comes live when the 3 port valve is operated.

Thanks again
Stuart

 

[D_Hailsham]

I understand the permanent live feed from the fused spur goes to the boiler

That's good.

the feed to the wiring centre comes from terminal 1 at the boiler to (I assume) the live supply terminal in the wc.

Don't assume - check!

The wiring centre needs Live, Neutral and Earth connections; where do they come from and which terminals do they connect to in the WC?

Which terminal in the WC is the wire from boiler terminal 1 connected to?

The time clock ... would be wired into the wc.

That's OK

Where does the switched live come back to the boiler from (position 2 on the boiler), is it the live that should go to the pump ?
as this comes live when the 3 port valve is operated.

The pump is inside the boiler and wired internally. Do you have a second pump currently wired to the wiring centre? If you don't, you can forget all about the pump wiring.

Please answer the questions in bold.

 

[NORDENHEATING]

Thanks Again.

No seperate pump, just system pump.
Live out from boiler actually terminal 2 going to terminal 1 in the wiring centre (live supply)

Terminal 1 in the boiler is the switched live back to the boiler.
Boiler wiring

L
N Wiring from fused spur
E

2 Feed out
1 switched live back to boiler from external controls


Wiring Centre wiring as follows

L - 1
N - 2
E - 3

Programmer
L - 1
N - 2
E - 3
1 - 8
2 -
3 - 6
4 - 4

3 Port Valve
W - 5
GR - 8
OR - 7
BL - 2
YG - 3

There is also the room stat wired to 2, 4 , 5 and the cylinder stat wired to 8, 6, 7.

Also stated, (just noticed) 'if you have a pump overrun on your boiler ...... Switched live supply connected to Terminal 7 in the junction box' is this the supply back to terminal 1 on the boiler?

Sorry for the long winded reply.

 

[D_Hailsham]

Sorry for not replying sooner.

Live out from boiler actually terminal 2 going to terminal 1 in the wiring centre (live supply)

I have just checked all the Megaflow manuals and all but one show 2 as the Live and 1 as the switched Live. I must have read up the manual with the exception!

Wiring Centre wiring as follows

L - 1
N - 2
E - 3

If the Live to WC terminal 1 is coming from the boiler terminal 2, where do the N and E come from?

The Programmer, 3 Port Valve, room stat and cylinder stat are all wired as expected.

'if you have a pump overrun on your boiler ...... Switched live supply connected to Terminal 7 in the junction box' is this the supply back to terminal 1 on the boiler?

Forget what it says about the pump overrun; your pump is wired directly into the boiler not to the wiring centre.

You just need a connection from WC terminal 7 in the wiring centre back to the boiler's Switched Live connection, terminal 1.

 

[NORDENHEATING]

Thanks D_Hailsham,

Ref last reply, would be using 4 or 5 core from the boiler.

N E , Terminal 2 on boiler connection to WC Live (1) (L,N,E)
terminal 1 on boiler connection (switched live back to boiler) from terminal 7 in the WC.

Only quoted the wiring centre instructions re the pump overrun to note that I had found this as the live back to the boiler.

I KNOW THE PUMP IS IN THE BOILER, THAT WAS THE INITIAL BIT THAT WAS THROWING ME.

Thanks again for the assistance. Needed to get it straight in my mind before starting on Saturday

 

[DP]

Boiler requires 240 volts on 2 to be linked to terminal 1 (Sl). Live, neutral or earth are there to keep the pump running if the boiler gets too hot.

If two port valves are used, the aux switch within the valve can link terminal 1 and 2. External 240 volts is not applied to 1 as the motorised valve provides volt free switching to link 1 and 2

This is not the case with 3 port valve if live neutral and earth is sourced from the spur or mains termination on the boiler. If power is sourced thus, boiler can be switched off at the boiler control panel, but programmer can apply 240 on 1 making the boiler controls live. Absence of neutral does not allow the boiler to run but every mains connection including neutral within the boiler will be at 240 volts. Good chance of getting fried. Sourcing 240 from 2 puts control of programmer via boiler on/ off switch.

 

[D_Hailsham]

Boiler does not have a switched live but presence of a loop/ link on 1 and 2 is required to run the boiler (see baxi solo connections for further explanation). Live, neutral or earth are there to keep the pump running if the boiler gets too hot.

The Baxi Megaflow uses switched 230v as in this diagram from the installation manual:

Untitled

• D_Hailsham
• 21 Feb 2009
• 1

Terminal 2 is live and terminal 1 is switched live.

 

[DP]

My earlier post now edited

 

[D_Hailsham]

This is not the case with 3 port valve if live neutral and earth is sourced from the spur or mains termination on the boiler. If power is sourced thus, boiler can be switched off at the boiler control panel, but programmer can apply 240 on 1 making the boiler controls live.

Only if the programmer is not supplied from the wiring centre, which is not the case. The OP is also taking neutral and earth from the boiler.

Good chance of getting fried. Sourcing 240 from 2 puts control of programmer via boiler on/ off switch.

Which is why I said the power to the wiring centre should come from the boiler. When power is turned off to or at the boiler, the wiring centre and everything attached to it will be made safe. The last thing anyone should do is have the isolator for the boil separate from that for the controls.

 

[DP]

Spur supplies 240 to terminals 1, 2 and 3 (earth) on WC. These are then extended to terminals L, N and E on the boiler and programmer. Above three points remain at 240 volts even when boiler is switched off.

Meanwhile the programmer can still extend live to boiler if a three port midposition valve is used.

Am I missing something? Have seen this scenario many times.

 

[D_Hailsham]

Yes that's correct.

It does not matter if you do it the other way round - spur to boiler, boiler to WC, WC to components.

In both cases, if you do not turn off at the spur, something can be live, even if the boiler is off.

The worst situation is where the boiler is fed from one spur, with the WC and components fed from another.