Grundfos 15/60 Pumping Downwards

[iwbnwif]

I am just about to replace a 22 year old and very noisy Grundfos 15/60 with a new pump (the same model). All other components in the unpressurised vented system are as installed by the house builder in 1989. Everything has been cleaned, flushed inhibited etc.

In the install instructions it says the pump should ideally be mounted vertically pumping UPWARDS however the existing pump is fitted pumping DOWNWARDS.

Now I am worried that the noise problem is caused by air in the pump (cavitation?) and the new pump will have the same problem. Obviously turning the pump upside down is not an option cos then the boiler flow and return will be swapped.

There is an automatic air valve but its on the hot tank side of the diverter valve. Grundfos say this must be before the pump and effective (their bold type).

Does anyone have experience of Grunfos pumping downwards? How do I tell if the automatic air valve is still effective after this time?

 

[45yearsagasman]

Pumping downwards is no problem.Cavitation is not common and I would check the cold feed,open vent connections are not restricted and causing air to be pulled in.

 

[iwbnwif]

Thanks for the reply.

The cold vent is fine, have recently flushed run X400 for a month flushed a couple more times and added X100. Each time it fills fine and starts running. Have checked the vent pipe (which returns to the cold water tank instead of the expansion tank) and it seems clear as far as I can tell.

There doesn't seem to be any air in the system, when the rads first fill then there is a "running water" noise, but after bleeding and running for a few days it quietens down. So I guess the automatic air vent is doing its thing?

Well hoping its just a worn bearing in the pump and the new pump will be quiet like in the old days

 

[doitall]

Don't like the sound of the heating vent pipe being over the domestic tank.

 

[45yearsagasman]

Yes I agree. May be misunderstanding of cold feed and vent pipe terminology. OP the only pipe that should terminate over your main storage water tank is the vent pipe from the top of your cylinder. The heating circuit vent pipe should terminate over the small expansion tank and NOWHERE else

 

[iwbnwif]

Sorry yes you are right, the vent over the domestic water tank comes from the top of the hot water cylinder

On the other hand that means there is no vent from the central heating, just expansion via the cold feed pipe from the small header tank.

 

[45yearsagasman]

Quote:-just expansion via the cold feed pipe from the small header tank.
Yes thats a combined feed and vent and should be 22mm pipe.

 

[Axel]

Sealed system with make-up-vessel?

 

[iwbnwif]

@45yearsagasman Yep 22mm pipe.

Basically everything is working fine, just a noisy pump. I hope it is a bearing, but I was a bit put off by the bold wording in the installation instructions regarding installation pumping downwards and the need for an effective air purger before the pump.

 

[Servotech]

@45yearsagasman Yep 22mm pipe.

Basically everything is working fine, just a noisy pump. I hope it is a bearing, but I was a bit put off by the bold wording in the installation instructions regarding installation pumping downwards and the need for an effective air purger before the pump.

I think that you maybe getting confused with the wording on the pump intstuctions.

When the pump is fitted horizontally the shaft should be level or at a slight slant in an upwards direction.
Having the shaft mounted downwards/upwards/verticle is a great causer of ecessive pump noise.
Roger,

 

[iwbnwif]

Thanks for all the help,

The instructions seem quite clear that it is preferable to mount the pump vertically. They do describe that if mounting horizontally then its necessary to be perfectly level or a slight slant in the upwards direction.

See here for the instructions, point number 1 at the top of page 4.

http://www.screwfix.com/prods/67637...mps/Grundfos-15-60-Domestic-Circulating-Pump#

Edit: Ah, sorry seems I can't link directly to the manual. The link is about halfway down the page just below "Specifications"

 

[mysteryman]

The pump spindle should be horizontal, or just above the horizontal if on a horizontal pipe. Pumping down is not to be preferred, because it can be difficult to clear the system of air. However, a 22 year life for a pump is quite good, and you can't do anything much about it anyway, so just replace it and you should be OK.

 

[Agile]

Presumably you have bled air from the pump?

To save time you can probably just change the pump head as held on with allen cap bolts.

But you do need proper pump valves of the gate valve type and NOT the screw driver slot kind which almost always leak!

Tony

 

[iwbnwif]

There are the proper pump valves installed already, so I am hoping it will be a fairly straightforward replacement job - no need to drain the system.

Yes, I have bled the air out of the pump but that doesn't make any difference.

I will give it a go this weekend and see what happens. If not its going to be quite a job to reverse the pipework to the boiler in a really confined airing cupboard

 

[D_Hailsham]

Basically everything is working fine, just a noisy pump. I hope it is a bearing, but I was a bit put off by the bold wording in the installation instructions regarding installation pumping downwards and the need for an effective air purger before the pump.

The standard vent pipe is sufficient.

The static head (vertical distance from water level in F&E tank to pump inlet) should be at least 1.4 metres.