/ Central heating pump direction

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captain paranoia 18 May 2019

Grundfos pump has seized (no complaint; it's been working for at least 17 years...).

But it's installed so that the electric access (in particular the speed selector) is underneath the pump, which is mounted part way into the attic flooring, in a cutout.

IIRC, they have to be mounted horizontally, but my question is, can I rotate it by 180 degrees, so the flow is the other direction?

I'm guessing the conventional glow is from the boiler hot output back to the cold input, so the pump works with gravity flow.

Any thoughts/guidance?

krikoman 18 May 2019
In reply to captain paranoia:

Why not just spin it around  so the speed selector is on top?

Ours is vertical by the way, and sucks water out of the boiler.

Robert Durran 18 May 2019
In reply to captain paranoia:

I don't understand the question, but I am sitting next to a crazy plumber in the pub and she says "of course not!".

1
krikoman 18 May 2019
In reply to captain paranoia:

Reversing the flow is not a good idea, the boiler needs to have flow the correct direction, to be safe.

captain paranoia 18 May 2019
In reply to krikoman:

> Why not just spin it around  so the speed selector is on top?

Fitted in stupid place, so structural wooden beam in the way...

captain paranoia 18 May 2019
In reply to krikoman:

> the boiler needs to have flow the correct direction

Okay; that makes sense.

As it happens, it looked like a direct replacement was available from Screwfix

https://www.screwfix.com/p/grundfos-ups2-15-50-60-central-heating-pump/42635

only not in stock, and no restock plan; looks like it's obsolete. Replaced with one with an electronic control, mounted on the front face. Problem solved... Pump now fitted and running.

Next job; find out why the immersion heater isn't working (haven't used it in years, only for it not to work when needed...). My guess is the element has corroded, although the breaker hasn't tripped.

Job after that: sort out the utter rat's nest of wiring for the CH controller, pump, stat & 3-way valve. It works, so I've never touched it, but it offends me... It wouldn't pass wiring regs, for sure...

captain paranoia 18 May 2019
In reply to krikoman:

> Ours is vertical by the way

I meant the axis of the motor; instruction pictograms confirm this. Water routing can be horizontal or vertical, but the motor axis must be horizontal.

captain paranoia 18 May 2019
In reply to captain paranoia:

Amazingly, it looks like the leads for the starter capacitor in the old pump were only press fit. Cap itself looks in perfect condition, which is one potential cause of failure. May dismantle old pump to see how it failed...

Mark Edwards 18 May 2019
In reply to captain paranoia:

> IIRC, they have to be mounted horizontally

Sorry for the hijack, but why do they have to be mounted horizontally?

The pump on my solid fuel central heating is mounted this way and it is an air trap. I am going to be moving it soon and have decided to fit it vertically with a self bleeding drain at the highest point to stop the occasional knocking when air is trapped in it. Is there a reason to why it should be horizontally as I can’t see why?

Steve Clark 18 May 2019
In reply to Mark Edwards:

You can mount the pipework horizontally or vertically, but the shaft of the motor should be horizontal. This allows it to self purge of air into the general system rather than trapping it in the pump. If you mount the shaft vertically, the top bearing can run dry.

Download a grundfos manual and it has some diagrams. 

marsbar 18 May 2019
In reply to captain paranoia:

If you don't have a diagram and it's working fine may I respectfully suggest you leave the wiring well alone.  

captain paranoia 18 May 2019
In reply to marsbar:

That's the approach I've taken for the last 17 years. But, as an electronic engineer, the mess of wires and single chock block connectors offends me. Diagrams are available, but they aren't the clearest. I've taken photos of the existing setup, and may sit down and figure out how it's wired, and tidy it up nicely. Maybe at some point in the next 17 years...

captain paranoia 18 May 2019
In reply to Steve Clark:

> If you mount the shaft vertically, the top bearing can run dry.

That was my understanding, too.

Mark Edwards 19 May 2019
In reply to Steve Clark:

Thanks for clearing that up. Currently the motor shaft is vertical but in about 35 years I only had to replace it once, but will put a new one in when I move it in case the bearing has worn.

captain paranoia 21 May 2019
In reply to captain paranoia:

Having dismantled the old pump, it may well be that it just needed a good clean, to remove black oxide deposits (copper or iron; not sure). Still a bit rough turning, but, considering there's a date code 11/91 on the starter capacitor, it's been in service for about 28 years, it's not doing badly. Interesting construction and drive; I may have to look up how the motor works.

Just a heads up for anyone with the same problem; four allen-headed engineering bolts allow the pump to be dismantled (and the orientation of the electrics changed, to answer the original question...). The rotor pulls out of the stator assembly. Bit of manual and brush attention, and the seized rotor can be cleared. Save yourself £100-£135, perhaps. Or at least, buy yourself some time before it needs replacing.

May mothball for 28 years, assuming the replacement lasts the same time...

duchessofmalfi 21 May 2019

Don't reverse the flow.

If it is an open system the breather / expansion tube may move from the low pressure side to high pressure side and you could dump water .

Either way the heat exchanger will be designed to work with the flow in one direction and may be less efficient in the other.

krikoman 21 May 2019
In reply to captain paranoia:

> Just a heads up for anyone with the same problem; four allen-headed engineering bolts allow the pump to be dismantled (and the orientation of the electrics changed, to answer the original question...). The rotor pulls out of the stator assembly. Bit of manual and brush attention, and the seized rotor can be cleared. Save yourself £100-£135, perhaps. Or at least, buy yourself some time before it needs replacing.

Sorry I should have suggested that, the pumps can get clogged quite easily and don't have  a lot of torque to start sometimes an old fashions Birmingham adjustment (with a hammer) is enough to get them running again.

at least you'll know for next time, the new pump won't last for 28 years, I can almost guarantee it.

captain paranoia 21 May 2019
In reply to krikoman:

> the new pump won't last for 28 years, I can almost guarantee it.

It's another Grundfos. The impeller housing and motor look identical. The main difference is the electrics, with an electronic control; my guess is that will fail...

BTW, the starter capacitor on the old pump has push-fit leads. They're still shiny. But, in removing one to inspect, I failed to note which hole it came from. Any ideas? There are about five holes. I used wire length to judge which one it looked like it ought to go in...

[edit] Google to the rescue...

https://www.homeownershub.com/uk-diy/capicitor-wiring-for-a-grundfos-ch-pump-121604-.htm

Post edited at 11:08
krikoman 21 May 2019
In reply to captain paranoia:

> > the new pump won't last for 28 years, I can almost guarantee it.

> It's another Grundfos. The impeller housing and motor look identical. The main difference is the electrics, with an electronic control; my guess is that will fail...

> BTW, the starter capacitor on the old pump has push-fit leads. They're still shiny. But, in removing one to inspect, I failed to note which hole it came from. Any ideas? There are about five holes. I used wire length to judge which one it looked like it ought to go in...


I'll see if I can find out, for you.

captain paranoia 21 May 2019
In reply to krikoman:

Thanks; Google seems to have come up with the answer; holes 4&8

krikoman 21 May 2019
In reply to captain paranoia:

> Thanks; Google seems to have come up with the answer; holes 4&8


two of my favourites


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