Setting bypass valve

[F]

After changing a couple of radiators, air has collected adjacent to the bypass valve (stamped USV16/22) creating a low buzzing noise. I've opened it and the air has moved on but I omitted to look at the number it was set to.

Is there a 'standard' setting? '1'? '7'?

I don't quite see why we've got/need one as both DHW and CH circuits are controlled by motorised valves and one of the radiators doesn't have a TRV and so can act as a bypass.

[John Rumm]

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:

with both valves closed, there is no path through either rads or cylinder - hence the need for a bypass if you system also has pump overrun.

[Andrew Gabriel]

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.

[Fredxx]

I was going to say look here

for the spec of the bypass settings, and then look for the pressure vs flow for each speed of the pump you have.

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

[F]

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?

[ARWadsworth]

Any ideas how does this bypass inhibits rust?

[ARWadsworth]

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

[Andrew Gabriel]

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

[F]

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.

[John Rumm]

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.

[ARWadsworth]

I also found this.

I was enjoying not going to work today.

Adam