Bypass valve? What does it do?

[Olivias Grumpy]

Hello
I’ve replced bypass valve with a new ABV. Set at default 0.2 bar
Vastly improved the circulation problem.
However I’m not sure how to calculate the best setting for the valve to assist the system.
Can anyone help with this please?
Thanks

 

[Terry lambert]

God advice on checking with a magnet around your cold feed as if partially blocked this will cause circulation issues, common fault

What pump do you have and on what setting

 

[John D v2.0]

Basically set it so when all/most the rads are closed the bypass is open, ie a bit lower than the pump head. If there's noise from the rads then open a little more.
If there's not enough flow through the far rads close a bit more.
If you can't get flow it could be the pump needs turning up.

 

[Terry lambert]

Basically set it so when all/most the rads are closed the bypass is open, ie a bit lower than the pump head. If there's noise from the rads then open a little more.
If there's not enough flow through the far rads close a bit more.
If you can't get flow it could be the pump needs turning up.

Nope

 

[Olivias Grumpy]

Hello terry. ( first response)
I have checked with a magnet where described. No evidence of a blockage using this method

Pump is Grundfos alpha 2L
Set on highest of constant settings at present

Could you explain more about second response? “Nope” doesn’t tell me a lot

Thanks

Hello John D
Thanks for reply , I’ll need to read up a bit I believe on pump spec etc

Thanks

 

[John D v2.0]

Olivias, also no idea about nope, but the idea of a bypass is to ensure the head from the pump is pushing water through the heating circuit when there's a demand, but when most of the rads are closed off the water can still flow quickly enough through the boiler to avoid noise and overheating etc.
Automatic bypass will open and close based on the pressure, fixed will just let some through all the time. The pump only has a certain head at the flow rate your boiler needs on whatever setting it's on, so you'd always set it lower than that, but too low and it'll let water through when not necessary.
But in reality it's not an exact science, if it works it works

 

[Olivias Grumpy]

Thanks for detail
I understand the theory etc
How do I find “flow rate” and “required head”

I’m sure at present it’s set too low, but I don’t want to screw it in too high. Or is it trial and error?

Cheers

 

[John D v2.0]

If it were me I'd open all the rads, turn on the boiler, and make sure there's no flow through the bypass (doesn't get hot on the exit side). That means it's all going through the rads.
You can tweak with trial and error but that proves it's not set too low.

 

[Terry lambert]

There should be instructions with your auto bypass but it needs to be set for the minimum flow rate of the pump curve your system requires, you then need to check that this meets the minimum flow rate of your boiler

Then check this against the chart in your auto bypass instructions for the correct setting

For instance

http://www.honeywelluk.com/documents/Installation-Guide/pdf/950.pdf

 

[Terry lambert]

These graphs are in the instructions for your boiler and pump

 

[Terry lambert]

Olivias, also no idea about nope, but the idea of a bypass is to ensure the head from the pump is pushing water through the heating circuit when there's a demand, but when most of the rads are closed off the water can still flow quickly enough through the boiler to avoid noise and overheating etc.
Automatic bypass will open and close based on the pressure, fixed will just let some through all the time. The pump only has a certain head at the flow rate your boiler needs on whatever setting it's on, so you'd always set it lower than that, but too low and it'll let water through when not necessary.
But in reality it's not an exact science, if it works it works

Nope

 

[John D v2.0]

Nope

not very helpful if you don't elaborate

 

[Terry lambert]

John D

Follow the advice I’ve given to the OP and read the instructions on setting up a bypass

Also read the instructions for the pump on proportional or constant pressure

All the help is there, you just have to read it

 

[John D v2.0]

Thanks Terry, I see your way it'll end up on the tightest setting first time i.e. only open when essential, and no need for trial and error. I was just going for only just tight enough to prevent bypass with full demand which may not be optimal.
I'll bear that in mind for next time. Thanks again, John

 

[Terry lambert]

Have a read here, the process is quite well explained

https://www.pegleryorkshire.co.uk/M...003/89827351_Terrier_By-pass_valve_678021.pdf