Is it better to wire the pump independent of or fed from the boiler?

[Bordonbert]

It seems a simple question so I hope this is enough info to require only a simple answer for you guys to give.

I have an existing installation which was recently upgraded with a new Worcester Greenstar 15Ri boiler. The system is small and is pretty standard open vented with a single zone. Everything is wired into a single Wiring Centre type connection box in an upstairs airing cupboard. This is also where the hot water storage tank, controller, wireless thermostat receiver, pump and routing/zone valve (used only for HW/CH selection) are physically situated. The boiler and wired room stat (used only for default minimum setting) are the only components downstairs with the boiler in a nearby large utility cupboard. Every one of the individual components of the system are wired separately directly into that connection box. It all seems to work perfectly as it is now wired.

The pump is controlled direct from its own switch in the timer/control unit as is the boiler. However, I know that the new boiler manual shows the pump wiring as being Controller -> Boiler -> Pump. i.e. the controller switches the boiler which is then feeding the pump which is logical as the pump action is dependent on the boiler status. There seems no problem with the controller switching both boiler and pump separately but linked time wise as poles of the same relay. However, I realise it may not be the most efficient way to control the two in energy terms.

It did occur to me that there may be some modern advantage, perhaps delayed switch off or something of the sort, which would mean that allowing the boiler to control the pump would have definite advantages. Would there be any practical advantage to adding a cable between pump and boiler and rewiring the pump to match the wiring schematic in the manual?

 

[steadyon]

1. The boiler controls the pump to provide what is called "pump overrun".
2. The purpose of pump overrun is to circulate water for a while after the boiler turns off, to prevent the residual heat in the main heat exchanger overheating the water.
3. If you rewire it to obviate pump overrun you may well damage the boiler and will void the warranty.

 

[Murdoch]

Central heating should have a single point of isolation for all components

 

[Brambles]

I would get the installer back and ask him / her to rewire the installation in accordance with the manufacturers instructions. Whilst the pump is mounted externally, control (of the pump) should be via the boiler PCB

 

[Bordonbert]

I thought it would be good manners to give an update to round this off as people had been kind enough to respond.

I have now taken the cover off the boiler to investigate what would be necessary, (JUST the main outer skin and the small plastic inner electrical cover for access to the connections, nothing else touched in any way). What I found surprised me. The pump terminals were already populated. I checked these wires through to the incoming cable from the controller installation area.

I then went back to the old wiring installation in the upstairs airing cupboard at the controller and looked more carefully there. This is currently not a standard interconnect installation by any means. It works and it chases out logically but it is not a simple clear thing to check as you guys seem to be able to do with your default layouts. The cable from the boiler, which looked like plain 3 core mains cable, is in fact more correct 5 core with a black and grey/white. The wiring is so tight that the grey/white and black were lost behind other cabling so it was not obvious that the pump was being fed from the boiler. That cable looked like plain 3 core mains.

It's a relief to know that it is correctly installed after all and I thank those guys who advised that that is an essential part of fitting. I will be addressing the wiring and updating it to a more "proper" wiring box and to a standard format asap.

Thanks for the help, it was much appreciated.