No pump speed adjustment on Baxi boiler?

[jacoscar]

I was looking for the pump speed selector on the side of my Baxi Boiler’s pump; the pump is a Grundfos 15 60, there is nothing to select the pump speed

The reason I’m asking is that I’ve installed smart TRV so there will be moments where only one radiator is working

Not sure if pump speed should be reduced in this case...

 

[ianmcd]

which baxi boiler

 

[jacoscar]

which baxi boiler

Baxi Duo-Tec Combi 28 HE A

 

[ianmcd]

Nope you can not adjust it, it has an erp pump it will adjust itself

 

[jacoscar]

I can hear the water circulating inside some of the radiators; I though this might be due to the pump speed

 

[ianmcd]

you cant alter it

 

[jacoscar]

I have noticed that if I turn on all the Tado valves together the water noise is acceptable, but as soon as I leave only one open, the noise is very loud

it sounds like the pump is not adjusting its speed...

 

[muggles]

Might be an older fixed-speed type then, in which case it is what it is.

 

[Gasguru]

The pump is fixed speed on this model...consider fitting an external auto bypass across the flow and return.

 

[jacoscar]

The pump is fixed speed on this model...consider fitting an external auto bypass across the flow and return.

I assumed the boiler had an automatic bypass valve built in

 

[durhamplumber]

The pump is fixed speed on this model...consider fitting an external auto bypass across the flow and return.

And gain what?

 

[Gasguru]

The fixed boiler bypass is relatively small and really only designed for heat exchanger protection...an external bypass will relieve differential pressure across the flow and return once the rads shut down.

 

[jacoscar]

The fixed boiler bypass is relatively small and really only designed for heat exchanger protection...an external bypass will relieve differential pressure across the flow and return once the rads shut down.

wouldn’t a bathroom radiator with valves fully open achieve the same result? Apart from wasting more energy

 

[durhamplumber]

The fixed boiler bypass is relatively small and really only designed for heat exchanger protection...an external bypass will relieve differential pressure across the flow and return once the rads shut down.

How does that help anything?

 

[Gasguru]

The pump is dumb and runs at a set speed....the pump will always operate at a point somewhere along its "pump curve" ie. the line showing the relationship between flowrate and available pump head (pressure).
As you close down the radiator valves the operating point on the pump curve moves leftwards and upwards with a reduction in flowrate and an increase in pressure across the system.
For example if you were foolish to shut all the valves (ignoring the boiler internal bypass) the pump would be "deadheaded" and with zero flowrate the head pressure would top out at around 5 or 6m depending on the pump fitted.
Having a towel radiator open would drop the operating point back down the curve a little and likewise the excessive pressure could be relieved by the opening of an automatic spring loaded bypass valve (adjusted accordingly).