Noisy System

[RP61973]

Any ideas? The circ pump on my central heating system (Grundfos) is positioned around 1.6m above the hot water outlet of the boiler. When the pump is running it sounds as if the pump gets so far then a column of water falls back into the boiler and then the pump lets out an almighty snore. To me it sounds as if the NPSHR to allow the pump to operate correctly exceeds the NPSHA due to the 1.6m difference. I am not sure what model of Grundfos pump it is (it is a 3 speeder and red in colour, I will need to creep up in the cold loft!) but adjusting the speeds makes no difference to noise.

Is the NPSHR theory possibly the case or am I talking b*llocks?

Any replies/ideas received are much appreciated.

 

[spacethegas]

 

[RP61973]

Spacethegas - what section of my post is unclear?

 

[spacethegas]

NPSHR & NPSHA

sounds like air perhaps ?

more details on the system & its controls req.

sealed or open vent ?

does ch/hw work etc.

 

[RP61973]

Net Positive Suction Head Required and Net Positive Suction Head Available.

NPSHR is the suction pressure necesary to ensure correct pump operation.

I have bled the air out of the system (bleed points on both sides of the 3 position valve) over a period of 1-2 days and there is no more air wanting to come out. This is a long-term problem that I have ignored for the past few years of owning the house but want to fix now given that I have just replaced the 3 position valve which decided to give up.

HW and CH work well - it is an open vent system.

I am just unsure what the charateristics of the Grunfos pump are, i.e. what the 'lift' capability is on the 'pull' side. I am aware they are able to 'push' up to around 6m. Or is it the case the pump should have been fitted nearer the boiler?

 

[spacethegas]

it makes no difference where the pump is fitted as long as it is on the flow between the blr & 3 port.

 

[RP61973]

OK, could it be a problem with the pump or the boiler? As I say all seems to work OK (although when I replaced the 3 position valve, one of the rad circuits took ages to start functioning (6 hours) although the other circuit feeding the lounge and 1st bedroom started immediately). I have bled the pipes either side of the 3 position valve (bleed nipples on top) to no avail. If it is air there sounds like a whole load in there that seems to be trapped at the location of the pump (which is only about 1 foot away from the 3 position valve bleed nipples).

 

[RP61973]

BTW I am running a Stelrad Mexico boiler - seems to be a good little unit.

 

[spacethegas]

blrs good.

in the op you mention the pump is in the loft.

can you do a line diagram of the exact configuration.

i assume it is open vent.

 

[JohnD]

I have bled the air out of the system (bleed points on both sides of the 3 position valve) over a period of 1-2 days and there is no more air wanting to come out.

do you mean it stops bleeding, or do you mean water squirts out vigorously, even from the highest radiator in the house?

this is very important.

and is the highest radiator higher or lower than the pump?

how high is the pump compared to the F&E?

 

[RP61973]

JohnD - When I bleed all radiators, water squirts out vigorously. Also when I bleed the 2 bleed points (1 either side of the 3 position valve) just water comes out, no air. The 2 bleed points are the highest points on the pumped system.

Spacethegas - It is an open vented system.

BTW I live in a bungalow - I will sketch the system and post it here.

 

[RP61973]

Herewith sketch of my CH/HW system (apologies for the rough sketching)

 

[spacethegas]

hopefully you've made a few errors on your diagram (good effort by the way).

the vent from the top of the cylinder should exit over the cold water storage tank.

there should be a vent over the feed & expansion tank from the primary side.

you show two pipes coming from the f/e tank ?

 

[JohnD]

the pipe you have marked boiler return shouldn't be as drawn. it looks higher than the tank (so will be full of air)_ and you show it coming of the cylinder vent, it should come out of the side of the cylinder near the bottom

Hot to bath, basin and sink should come from the top of the cylinder, not the bottom.

 

[spacethegas]

the pipe you have marked boiler return shouldn't be as drawn. it looks higher than the tank (so will be full of air)_ and you show it coming of the cylinder vent, it should come out of the side of the cylinder near the bottom

Hot to bath, basin and sink should come from the top of the cylinder, not the bottom.

i just think he got these two the wrong way round.