Grundfos Magna Installation - Achieving downward flow

[nichbull]

Over the weekend I redid all the piping under my house to insulate it, make the runs simpler and install a drainage point. In short to bring it up to code. I have also installed a new pump as the old pump that was installed was undersized and could not run the central heating with the underfloor heating at the same time, however well I balanced it. The boiler I have is Glowworm Hx which I understand from forums here has a relatively high resistance and the pump could simply not develop the required flow rate for the boiler. The boiler would go into tickover mode repeatedly when both the central heating and underfloor were running together as the temperature difference between the outbound temp and inbound boiler temp would become too great and it would then tick over for a few minutes before firing again. The practical result of this meant lukewarm radiators when the underfloor was on!

I am currently pressure testing the repiped system cold to check I have no leaks before starting it up later this week. So far after 16 hours it is holding 1.5bar which is great news.

The question is this. The new pump that I have installed is the Grundfos Magna 180 25 100 as I got a good deal on it. (They are currently replacing is with two different types of variable pumps as I am sure you are all aware so it is possible to get them slightly cheaper) following the new EU regs.

Re then the Grundfos Magna 180 25 100. Having worked so hard have I made a major mistake? My pipe run is such that the boiler is on the first floor and the pipe work for the heating therefore below it. The old pump was therefore installed upside down as the flow direction was downwards.

There is nothing to say in the technical instructions that the Grundfos Magna pump can not pump downwards. Have I missed something, can it? I have followed the installation directions and rotated the head of the pump 180 degrees in the case. This means the control panel faces the straightforward and ordinary directions upwards, but the pump back casing's arrow of flow direction is downwards. Is this correct way to install it or is my logic wrong? I have done this because of the instructions on it seemed to indicate that the control panel should not be installed pointing downwards and therefore logically deduced this was how you should install it to achieve my desired aim.

Have I just made an error and in fact is the pump like others designed by grundfos are simply not designed to pump downwards for fear of trapped air causing problems with it? All advice gratefully received!! I have googled, googled, and read all the technical documentation and can not find the answer.

 

[D_Hailsham]

Provided the static head (vertical distance from water level in the Feed and Expansion tank to the pump inlet) is more than 1.02m at 75C (3.6m at 95C), and there is an unrestricted path from the pump inlet to the open vent, you shouldn't have any problem.

The vent pipe should, preferably, be teed off an horizontal pipe, i.e like this:


[code:1]

Vent Feed Vent Feed
|| || || ||
|| || || ||
|| || || ||
================ NOT |===========
||
||
[/code:1]


I know it's a bit late now, but did you consider using a Low Loss Header and two smaller pumps?

Another option is using "Closely Spaced Tees"

View media item 57814
Both of these isolate the boiler circuit from the heating circui. You then use two smaller pumps, one for each circuit.

 

[nichbull]

Just to say thank you (and if I ever redo the system I will definitely think about a low loss header!). Pump working fine and Grundfos technical support confirmed you do rotate the pump head when pumping downwards.