Under sink water heaters

[Matt887]

Are the little 10 litre under sink water heaters ok piped up just places on the base of a unit/ the floor. Or is it best to mount to a wall under the unit? Thanks

 

[Mottie]

I've had a few of them in several workshops. None have been wall mounted, they just sit there. IIRC they have rubber pads on the bottom.

 

[ericmark]

I had one in a caravan, as @Mottie says, it just sat there. But was connected with flexible pipes.

 

[dilalio]

Some come with a wall bracket so I use it.

 

[Johntheo5]

Assuming there isn't a NRV in the mains supply which will prevent the expansion, what is the max capacity allowed without installing a EV??

 

[dilalio]

Assuming there isn't a NRV in the mains supply which will prevent the expansion, what is the max capacity allowed without installing a EV??

I used pipework for expansion for my one in the garden room. Can't remember the length required but it's in the MI's.
Mine is a 15L Ariston... Been down there for years now.

 

[Matt887]

Assuming there isn't a NRV in the mains supply which will prevent the expansion, what is the max capacity allowed without installing a EV??

I think it depends on the distance from the unit to the nearest cold water tap. A 5litre unit requires about 2 meters a 15 litre around for litres. Other wise it's a single check valve and 2 litre expansion vessel

 

[Johntheo5]

That sometimes creates a bit of confusion as one might think that the pipework itself can accomodate the expansion, say ~ 0.3L with a 15L cylinder but it must have no restriction right back to the mains like a PRV or a NRV, its only, IMO, to ensure hot water doesn't come out the cold tap. A friend of mine had a 10L with its own PRV, see below, (pressure relief valve) which would start feathering very shortly after he switched on the heating element, he found a PRV (pressure reducing valve) on the mains and just removed it as his mains pressure never exceeds 3.0bar.

The cylinder had a Ariston 571730 combined PRV & anti syphon valve.

 

[dilalio]

That sometimes creates a bit of confusion as one might think that the pipework itself can accomodate the expansion, say ~ 0.3L with a 15L cylinder but it must have no restriction right back to the mains like a PRV or a NRV, its only, IMO, to ensure hot water doesn't come out the cold tap. A friend of mine had a 10L with its own PRV, see below, (pressure relief valve) which would start feathering very shortly after he switched on the heating element, he found a PRV (pressure reducing valve) on the mains and just removed it as his mains pressure never exceeds 3.0bar.

The cylinder had a Ariston 571730 combined PRV & anti syphon valve.View attachment 420551

Diagrams in the MI's are usually very good and explanatory.

 

[Johntheo5]

Diagrams in the MI's are usually very good and explanatory.

I'm not so sure about that, the schematic below shows a pressure reducing valve but not a expansion vessel, the 2.8M or 4.2M required for expansion might give the impression that no expansion vessel is required, also the statement below can lead to confusion, IMO.

 

[dilalio]

Well I fitted mine with 2.5m of 22mm hep and no EV and it's been fine... Not discharged in 12 years.

 

[Johntheo5]

Have you a pressure reducing valve on its supply?.