Setting bypass valve

No standard - but it wants to be set stiff enough that it remains closed unless there is no other path through the system. However you don't want it so stiff that it causes pump over. So some experimentation may be required.

If you have a S Plan system with two motorised valves:

If you have two-port valves rather than a 3-port valve, there will be no flow path when they both shut, and the boiler still wants to circulate to dump heat.

The radiator without TRV might not have enough flow when system has been balanced to be the only bypass, and/or might still have a stop valve.

I was going to say look here

However Pegler Yorkshire seem to have no useful data on their website!!

Yes.

Ah! Does the WB Greenstar Ri have pump overrun?

In general, is it best to set the valve to a low number or high? Or in the middle of the range?

Any ideas how does this bypass inhibits rust?

The WB Ri does have a pump overrun.

On an s-plan if there is any banging when the pump is overruning then just open the valve a bit more.

Adam

exchanger, for a non-condensing boiler, by leaking hot water back into the return.

Thanks.

The noise I heard was, I assume, trapped air (ooer!) and went as soon as I opened the valve.

I'll set it mid-way and try to check it's not opening when the system is running.

If both valves close and the bypass is set too tight then the water flow will be interrupted - that may cause the water in the boiler to "kettle" and make a racket. It sounds like you may have it set about right. You can possibly also tell if the outlet side of it stays cool during normal operation.

I also found this.

Adam