Unvented (I think) water heater - installation question

[JohnnyRotting]

I have just grabbed an old used Bosch Tronic TR1500 water heater, the type to provide hot water at a sink where only cold is available. Stupidly i didn't look into it much before snatching the bargain! A few questions...

Some reviews online look worrisome, e.g. :

"Despite the pictures on the web site showing that this heater is connected between the water supply and a tap it cannot be used in that way.
The heater will not take any pressure and must be connected with the control valve on the inlet and the outlet going to an open end."

Even in the Bosch installation manual (https://www.manualslib.com/manual/1857862/Bosch-Tronic-1500-To-Series.html?page=9#manual) it says:

"The small water heater is only suitable for use with an open(unpressurised) and a single tap connection. The warm wateroutlet is used for pressure compensation and may only beconnected to suitable fittings (Order No BZ 13051 or BZ 13061for undersink appliances or BZ 11113 for oversink appliances).• The tap outlet must always remain free. Do not use perlators(diffusers) or shower taps."

Looks like I bought a lemon. Any advice as to how I can make it work, as I don't really understand the comments above found online. Thanks

 

[stem]

It's a fairly common design for cheap water heaters. In that to keep costs down, there is no provision for pressure relief required. This means that the outlet has to remain open at all times to allow for expansion of the water as it is heated up.

In operation, cold water is introduced into the heater, and that in turn displaces the hot water out of the permanently open tap.

As you have stated, special taps are available. They are known as "Vented Taps". They look like ordinary taps but are permanently open with the tap mechanism operating a cold water supply that feeds cold water directly into the heater instead, this then pushes the hot water out of the permanently open tap outlet.

One downside is, that because the water is heated whilst it is stored, the volume of water expands and comes out of the open tap, so when it's heating the water the tap can drip. It stops once the water is hot though.

 

[JohnnyRotting]

Brilliant explanation, thanks very much indeed.

So I suppose I can either dump it, or find one of these special taps. Will see if I can find a used "vented tap" on fleabay. thanks again

 

[JohnnyRotting]

Vented taps not easy to come by (cheaply!) Wondering if one of these would be a sneaky but functional workaround?! (If fitted on hot line from tank to sink. https://www.ebay.co.uk/itm/155223208267

 

[stem]

I doubt it, the clue is in the name "Air Bleed" so it's designed to vent air, not water and even if it did vent water what are you going to do with the water that comes out of it?

The unit says it needs to be open vented, so fitting anything else other than an open vent is likely to end badly.