Jumping gauge

[Whn1]

Pressure gauge on a combi jumps up half a bar immediately when hot outlet is opened and drops back down as soon as its closed?

What's the reason for this.

many many many many thanks, tony

 

[villa_tom]

Isn't it something with the gauge being on the positive side of the pump? Someone may correct me, but I think this is the reason.

Some boilers drop a slight bit when first operated as the gauge is on the negative side of the pump.

I maybe wrong, but its what I know to be true.

 

[Whn1]

Yea I know that one mate but I think it's the neg side of the pump, this isn't the case on this one as it only does it when a hot outlet is opened and not when the pump kicks in.

 

[Whn1]

Misread your Reply so ignore the first bit of mine.

 

[buckley plumb]

main he does this think gas mans answered this subject a while back.when in hw mode pump more restrictive due to flow through plate I think was the amswer

 

[zzzjim]

Just an ordinary combi with diverter valve ?

(I'm thinking harder work to get thru plate HEX--)
when it all gets diverted that way

" Just pure theory ,never seen it "

 

[Whn1]

It was a main actually seen a few over the years, but doesn't do it on all, just entered my mind now, hopefully gas man will be along soon to enlighten me.

 

[vern]

Pressure gauge on a combi jumps up half a bar immediately when hot outlet is opened and drops back down as soon as its closed?

What's the reason for this.

many many many many thanks, tony

Back pressure Tony.......same can happen on an S plan when it pumps round the ABV only

 

[Whn1]

So it is the restriction through the phex rather than around the system?

 

[buckley plumb]

from what I remember yes

 

[vern]

So it is the restriction through the phex rather than around the system?

Correct

 

[dancinplumba]

All baxis do this 🙂

 

[Whn1]

Ahhhh never usually catches my attention then, would one that rises significantly possibly point to a scaled phex?

 

[zzzjim]

a scaled phex?

One Question to ask,why sealed heating side of phex,
that water should not be getting changed too often ?

 

[Whn1]

Yayayaya just over thinking.. 😉

 

[zzzjim]

just over thinking.. 😉

I'm probably guilty too,if they have a bad leak,and keep topping up a plenty, but then all hottest parts should be most scaled up