Under sink water heater.

knightstyle

I am thinking of installing one and am not sure if I need an expansion vessel, check valve and pressure relief valve?  It will be 10L. 2Kw.

Nearlyold

The manufacturers fitting instructions will tell you what you need to fit by way of safety devices. 

Is that a generic diagram or one from the manufacturer of the heater you're thinking of fitting?

You can buy a kit with all the stuff you need like this 

ComicGeek

The expansion vessel is normally required, unless you have a long length of cold water pipework between the water heater and the nearest tap that can provide the expansion. The manufacturer should have a better installation diagram, that one is too vague. 

Below is the diagram for an Ariston model without expansion vessel:


And then the same model with expansion vessel:

I've never done one without the expansion vessel and all the valves as per fig 2, not worth taking the risk on an unvented unit.

knightstyle

Thanks, that makes it more complicated than I hoped for. Instructions say to check local regs. but I can't find any for 10l heaters, only 15L and above.

Defensivelynchpin

10l units usually need 3m of pipe before the first outlet (tap) and 4.5 m for a 15 l unit for expansion.

If the unit is in a cabinet under the sink, it will need an expansion vessel as there will not be enough pipe run for expansion in the pipes due to not having at least 3 or 4.5m 

ComicGeek

knightstyle said:

Thanks, that makes it more complicated than I hoped for. Instructions say to check local regs. but I can't find any for 10l heaters, only 15L and above.

You could use a vented water heater instead, which have an integral spout or need vented taps - these don't need separate expansion vessels, as they use the open outlets for expansion. There are under-sink or over-sink options - something like https://www.heatraesadia.com/products/cylinders-and-hot-water/electric-vented-storage/express

plumb1_2

ComicGeek said:

knightstyle said:

Thanks, that makes it more complicated than I hoped for. Instructions say to check local regs. but I can't find any for 10l heaters, only 15L and above.

You could use a vented water heater instead, which have an integral spout or need vented taps - these don't need separate expansion vessels, as they use the open outlets for expansion. There are under-sink or over-sink options - something like https://www.heatraesadia.com/products/cylinders-and-hot-water/electric-vented-storage/express

You could go with a vented tap, but with passed experience they can be a pain in the bum
not a great deal of choice, and if they do drip into the sink, people tend to try and tighten the head to try to stop them dripping ( which they are intended to do), not realising. Especially if the heater/tap is not in your own home.

Far better to go with the expansion vessel, it doesn’t have to be in the same cupboard, drill a hole into the next cupboard and pipe it up into there.