Discuss Grundfos Alpha Pump replacement in the Central Heating Forum area at PlumbersForums.net

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Hello, my Mothers heating failed in the recent UK cold snap. I found the pump was stuck. I have a question about pump orientation. The existing pump flows downwards. The manual for the proposed replacement recommends that it should pump upwards. This would involve rearranging the flow & return pipes which I want to avoid. The existing pump is just after the expansion pipe and it worked for many years pumping downwards. Why is it recommended for Grundfos Alpha to pump upwards? Is the Grundfos really not suitable for this system?

Advice on this and the viability of my proposed 'improvements' below gratefully received.

Thanks.

More info on the system :

It's a vented system with free standing gas boiler at ground level serving 10 rads with TRV's in a large Victorian house (high ceilings) and DHW coil in the cylinder. The pump is level with the boiler, just after the expansion vent pipe and pumps downwards. There is a manual bypass gate valve open 1 turn. There is also a manual gate valve to shut off the heating circuit when DHW only is needed. The system was installed in the early 1970's and regularly serviced by BG, who replaced various parts over the years, including the boiler and pump. The present boiler is a Gloworm Hideaway and the pump is a BG branded Myson Multihead 2. Pump waranty date is 300603, so I presume it has been in service since about the turn of the century. The feed header tank is upstairs, approx 6m above the pump.

I was able to free the pump by turning the spindle by hand and it then ran smoothly. However, the gate valves above and below the vertically mounted pump will not shut off fully and black water sprayed out of the pump spindle nut when loosened. Once I had the pump running there were various grating noises coming from the pipes and I think there must be sludge in the system. Sometimes I could hear the pump struggling. The pump has stuck again on several occasions and felt very hot. Turning by hand was always very stiff, like wadeing through treacle. Then it would just free up and run smoothly.

I am planning to flush the system with Sentinel X400 and replace the pump and valves. Also fit an electric zone valve to the heating circuit so DHW only can be selected on the programmer. Also to fit a vortex eliminator magnetic particle trap in the return pipe. The pump is rated 74W at medium speed so uses a lot of electricity. I am considering a Grundfos Alpha 2 for its better economy. However, this is an expensive pump so will take a while to show a saving. However, I can get a used one with 6 months warranty for similar price to a basic high energy new one and clean out the impeller housing myself. I just think the economics will work out better that way.

Thanks for reading. What do you guys reckon?
 
You sure that’s not the head placement ?

As the arrow on the side of the pump shows you direction of flow ?

Sounds like the bearing in the pump is shot

 
With the existing pump head placement, the manufacturers label is upside down. The electrical connection box is to the side. But the arrow on the body is definitely downwards. From the boiler to the heating pipes. Expansion pipe tee just above the pump. Feed from tank directly into the boiler via a separate pipe.
 
Have you got a snip of the page that suggests upward flow or a link to the install instructions as I don't believe I've ever seen a pump where the direction of flow is stated as upwards only.
 
Yes, here are some screenshots from the Grundfos Alpha 2 manual. They show the pump mounted vertical or horizontal. In the vertical orientation with the flow going upwards. I also read somewhere that pumping downwards was not recommended for this pump, however I can no longer find that link. But I am confused now, because I have since found another Grundfos manual for this product which shows the flow in either direction. So is pumping up or down really an issue?
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As long as the head is not in the positions shown with the red X with the motor shaft not horizontal, where it is likely to put extra strain on the shaft and bearings, or possibly airlock or collect debris, then the pump can be mounted to flow up, down or L-R / R-L at any angle.

If the picture 3.2.a is suggesting that the pump can only have flow upwards then the picture 3.2.b must be suggesting that the flow can also only be left to right, which would severely restrict the use this pump.
 
Given your situation with the pump needing to fit without changing pipes, it's clear why you're a bit cautious. The Grundfos Alpha usually pumps upwards for better performance, but your system worked well pumping downwards for years. Our advice? Talk to a local heating expert. They can look at your setup and see if the Grundfos can work without moving pipes. Sometimes, there are simple fixes or adjustments that can be made. This way, you can upgrade without big changes, keeping your system running smoothly. Plus, a professional can help make sure everything works just right.
 
As long as the head is not in the positions shown with the red X with the motor shaft not horizontal, where it is likely to put extra strain on the shaft and bearings, or possibly airlock or collect debris, then the pump can be mounted to flow up, down or L-R / R-L at any angle.

If the picture 3.2.a is suggesting that the pump can only have flow upwards then the picture 3.2.b must be suggesting that the flow can also only be left to right, which would severely restrict the use this pump.
Thanks, I take your point about horizontal flow direction as that shouldn't make a difference. I found the reference to upward flow only in another Grundfos manual. However, it is referring to a Alpha variant with air separator chamber. I can see that makes sense. Other Grundfos installation manuals for the Alpha 2/3 are ambiguous, showing the vertical flow as upwards but not actually saying that downwards is no good. There are also manuals that show the flow in either direction. Now someone else has said that upward flow gives better performance. I am interested to know why. Is it to do with purging air from the system?
 

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