Tanked Rotary Pumped Machines

Machines with a Rotary pump that are NOT Plumbed into the mains water supply

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Machines with a Rotary pump that can draw from an Internal tank, rather than having to be mains plumbed are much more common. This will lead to problems unless suitable water for the machine is used. e.g. a filter system or RO water as described below.

Rotary pumps won't stop water flowing back through them like a Vibe pump, so most if not all rotary pumped machines will have a one way valve to prevent backflow from boilers/heat exchanger. The problem of hard water is not really so apparent with plumbed in machines as the 2-3 bar mains pressure prevents flow back through the pump.

Tanked/Pourover rotary machines are more susceptible to hard water as this valve does scale up and it can scale up as quickly as 6 weeks in very hard water areas. Owners don't initially tend to notice it, as the effects are insidious e.g. on an HX machine the group may not be hot as normal, there may be a delay of a few seconds before water exits an empty group etc..Initially some owners rejoice in the fact that they are not having to do such a large cooling flush, but eventually it needs dealing with.

This means regular descaling of the Brew circuit (in hard water areas), which on double boilers is usually a more tedious affair than the steam boiler. As I have owned an Izzo Alex for years (and now a Duetto), I am well aware of the issue on Tanked Rotary pourovers. The answer really is to use water that will not cause scale, and to be aware that scale will form in areas where the water does not get hot (simply look at the spout of your cold water tap to see this).

The link below shows the anti backflow valve of an Izzo Alex and the procedure for cleaning after it scaled up particularly badly, it is typical of the valves used for this purpose.


I and many others with Tanked Rotary machines use RO water mixed with a little softened water to bring the TDS up to around 40 ppm, so it tastes OK and wont form scale. This means a whole house water softener and then RO the softened water for drinking and the Coffee machine….The RO water can be mixed with Hard water to bring the TDS up to 40ppm or so, but even at this low level, scale will eventually form, it may take nearly a year or more to affect the anti backflow valve and descaling can possibly be postponed to a once per annum job.

The other area that's worth considering is the expansion of water (around 4%) when heated in the brew boiler of a twin boiler machine and depending on boiler size e.g. 800cc it's likely to push nearly 28cc of water through the OPV every time its warmed up from cold, so eventually the OPV (which although not used for pressure regulation), might need attention on a long term basis to fix scale problems. Although I have not seen inside a GS3, I can't imagine they have any other way of dealing with the expansion of the brew boiler water…again you probably won't notice this because the OPV probably routes back to the tank. Of course if you plumb the machine in over a period of a month you will accumulate nearly a litre of water in the internal tank, so remember to check and empty it!

P.S. I stress the point, that if your plumbed, you won't notice it, unless of course you start drawing from a container for any reason.