Should pump overrun happen every time boiler switches off (Potterton Profile 80e)?

[stem]

Sorry I don't understand that I didn't say 4 cables, but 4 cores (or wires) that would connect to the boiler ie:

Core 1 = Live (permanent)
Core 2 = Neutral
Core 3 = Earth
Core 4 = Switched live from the controls

 

[ianmcd]

Which of the 4 cables powers the pump? Are you not missing one, the pump is elsewhere.

Not like you David, obviously the pump is powered from the boiler, but if the boiler does not have a permanent live how can it supply power to the pump when the switched live switches off , the pump obviously is wired from the boiler and will have a LNE supply from the boiler, the boiler will decide if the pump needs to O/Run, not sure what you are asking to be honest

 

[vulcancontinental]

I just look at it as 5 cores, L,N,E,SL,Pump live

 

[Mottie]

Surely the SL is the pump live when the regular switched pump live is off but the overrun needs to tell the pump to keep running, so just 4 cores to the boiler?

 

[stem]

Sometimes I like to run the pump directly from the boilers terminals L, N & E without going through the wiring centre, so a three core cable for that, and the aforesaid four core cable for the boiler L, N, E, SL. [3 and 4 core cables are readily available]

Nothing wrong of course with using 5 cores back to a junction box / wiring centre from the boiler to include the pump live. The pump can then pick up its N and E from there.

There's more than one way to skin a cat

Surely the SL is the pump live

The switched live goes off when the controls dictate that the boiler should go off as no more heat is required, but, the pump overrun needs to carry on, so the permanent live is switched via the boiler's internal circuitry to keep the pump running, so it remains live after the switched live has been erm...switched off.

 

[Harry Bloomfield]

Surely the SL is the pump live when the regular switched pump live is off but the overrun needs to tell the pump to keep running, so just 4 cores to the boiler?

No...
Permanent Live
Switched Live - to tell the boiler it needs to run / or instead a bus controlled system
Pump control switched live

Neutral
Earth

The Permanent Live is needed by many modern boilers to run the wireless module and maintain the built in frost protection.

 

[dilalio]

So many old installs have twin&earth with boiler only firing when switched... No good for digital displays and pump overruns... Triple&earth at the very least.

 

[ianmcd]

I just look at it as 5 cores, L,N,E,SL,Pump live

only if the pump live is coming from the wiring centre then yes I would wire it that way , but as the boiler has a LNE supply for the pump most installers of these old boilers ran a 3 core flex direct to the pump from the boiler