Dated info, but there certainly were, a great many Steibel Eltron heaters, both instant and near instant (very small capacity) supplying the bathrooms and kitchens of German flats in west Berlin, and later refurbished eastern ones too. Certainly the older models seemed to be pretty much bomb proof, and many I saw in service were  20- 30 years old then  (early 2000s) and still working,

If you have hard water that may not be the case but there is very little to say other than their old models work very well. Essentially those models were 3 resistors in a tank, a pressure drop flow switch and a bimetallic thermostat, I suspect that the 21st century will have added a blue LED and a microprocessor, which are probably the least reliable parts.

Installation instruction suggest 40A MCB

Mike

I installed a three phase instant water heater some years (10?) ago in a similar local facility. It supplied a massive commercial sink via the previously installed normal tap. It worked well and is still in use to date and I have not been told of any problems despite having a hard water supply. Unfortunately I cannot remember the make, but it was one of the larger manufacturers, or rating but probably 20A per phase. Far better in my opinion than the stored water alternative especially when usage is intermittent with a high volume required when it is used. 

Kevin

What's the water supply like? It can be difficult to get the full benefit of instantaneous water heating if the supply can't keep up. Just thinking that if the Hall's on the end of a long old 1/2" pipe...

   - Andy.

Thanks Mike, Kevin and Andy

Nothing adverse, so will get a quote or two for fitting etc.

Luckily the water is fairly soft and the supply pipe is 25mm MDPE fitted two years ago back to the water main when we got rid of the lead pipe.

I will not be doing the work, but for checking the quote,  5-core 6mm² SWA would seem to be an overkill, would H07RN-F again 5-core 6mm² be satisfactory? The cable would be running within an existing cable duct.

Thanks.

Clive

SWA would seem to be an overkill, would H07RN-F again 5-core 6mm² be satisfactory?

Any requirement for additional protection by 30mA RCD if the cable doesn't have a concentric c.p.c.? (e..g. cable duct concealed <50mm deep in a wall? These units seem to have bare elements immersed in the water, with no N connection (just PE), so I suspect there could potentially be some significant leakage current if everything isn't quite balanced.

   -  Andy.