What's this pipe for?

[Jonesminor]

We have a conventional boiler with vented hot water cylinder and two tanks in the loft. All the electrical gubbins is honeywell as is the 3 position port.

Trying to get my head round all the plumbing before I add a feed for the pumped shower and comparing to all the diagrams, I have an extra pipe. It tees off from the boiler hot return after the pump but before the AB of the valve and runs, via a gate valve, to another tee on the boiler return next to the bottom circ flange.

Is it to avoid damage to the pump if the valve is closed? I thought the valve was always at least open to A or B, returning to B with no voltage applied?

Thanks

 

[denso13]

Manual bypass to ensure the pump isn't working against a closed valve.

 

[Jonesminor]

Thanks for the info. Is the valve normally open or closed or something in between? Hard to tell with this one, all crud around it.
The gate valve, not the motorised.

Reason I ask as it's a candidate for being rerouted to make room for the pump and its feeds.

 

[flameport]

Is the valve normally open or closed or something in between?

Opened a tiny bit, to allow just enough flow when all radiators are closed, but not allow too much otherwise the radiators won't get much if any heat.

I thought the valve was always at least open to A or B

It is, however if at B and all of your radiators were closed (due to TRVs or a manual valve) the pump would have nowhere to circulate the water.
If at least one radiator is permanently open (doesn't have a TRV or a manual knob to close the valve), then you don't need the bypass . A towel rail was often used for that purpose.

 

[Jonesminor]

Thanks