Circulating Pump Flow Direction

[manton]

Any heating engineers here. The circulating pump on my fairly old oil heating system died and when I replaced it I noticed that although it was in the returm pipe it was pumping away from the boiler. Surely this cannot be correct  What would happen if I turned it round to pump into the boiler. Could it aause any calamities somewhere else in the system?

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[serrac]

Assuming the previous pump was pointing in the same direction and the heating was working OK, you may as well leave as is.

If you have thermostatic valves on your radiators they may rattle at times if the flow is in the opposite direction to what was expected when they were installed.

Also, if it's an open system with a header tank in the loft you may find the pump pushes water into the header tank rather than round the system as the pressure differential has reversed.

[old'un]

sounds like an open vented system as it as an external pump, ours is an open system and the pump is fitted to the boiler hot water out and pumps hot water around the rads and hot water tank.

Must admit the way yours is working does sound odd.

[manton]

3 hours ago, serrac said:

Assuming the previous pump was pointing in the same direction and the heating was working OK, you may as well leave as is.

If you have thermostatic valves on your radiators they may rattle at times if the flow is in the opposite direction to what was expected when they were installed.

Also, if it's an open system with a header tank in the loft you may find the pump pushes water into the header tank rather than round the system as the pressure differential has reversed.

Thank you for your reply which I found most informative. The last paragraph might  point toward an answer to what is happening, . I have  a noise like running water in the loft and a new radiator I fitted is stone  cold   The previous owner of the house said they had always had problems with that radiator. Is it possible that the  pressure of the pump is being wasted

Edited December 1, 2023 by manton
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[serrac]

On 01/12/2023 at 10:50, manton said:

Thank you for your reply which I found most informative. The last paragraph might  point toward an answer to what is happening, . I have  a noise like running water in the loft and a new radiator I fitted is stone  cold   The previous owner of the house said they had always had problems with that radiator. Is it possible that the  pressure of the pump is being wasted

You could try turning the pump round to try it in the other direction - there's normally valves on either side of it so you don't need to drain the system.  I'm sure you're aware of that since you fitted a new pump 🙂

The radiator not heating up sounds like an airlock in the system preventing hot water flowing through that one.
They can be a pig to get rid off because of course you can't see where they are hiding.
There's various videos in YouTube how to deal with them but the basic idea is to force water through the system expelling any air pockets.

Make sure your system has inhibitor in it as corrosion inside the radiators or boiler creates gas which can eventually form another airlock.

[Old Boggy]

2 hours ago, serrac said:

You could try turning the pump round to try it in the other direction - there's normally valves on either side of it so you don't need to drain the system.  I'm sure you're aware of that since you fitted a new pump 🙂

The radiator not heating up sounds like an airlock in the system preventing hot water flowing through that one.
They can be a pig to get rid off because of course you can't see where they are hiding.
There's various videos in YouTube how to deal with them but the basic idea is to force water through the system expelling any air pockets.

Make sure your system has inhibitor in it as corrosion inside the radiators or boiler creates gas which can eventually form another airlock.

The lack of inhibitor as said, can cause `Hydrogen Evolution` put simply is the oxidation of copper (pipework) or steel (radiators) taking out the oxygen to leave pure hydrogen. This is often mistaken for air in the system normally on the highest radiator but can determined by bleeding the radiator and applying a naked flame at the bleed point. If hydrogen this will give a small blue flame a bit like a tiny blow lamp. 

It also sounds as if the pump being reversed is now pumping over the vent, hence the `rushing` sound. It very much depends on the position of where the cold feed is connected to the system, known as `The Neutral Point`.

I would be inclined, as serrac says, to try turning the pump round.

OB