under sink instant hot water

[DH202020]

Hi all

Looking for a simple under sink instant hot water, direct mains fed

 

It's for the garage and will serve 2x sinks (not at the same time) Occasional use only

 

Any recommendations? looking at the cheaper end of the market

Thanks

David.

[ProDave]

I have fitted a couple of these for customers. They come in at least 3 different sizes. They seem to do the job for a sink in a kitchenette and a basin in the toilet.http://www.ebay.co.uk/itm/Hyco-SF10K-Undersink-Electric-Water-Heater-Unvented-10-Litre-2Kw-/290610639375?epid=1812691432&hash=item43a9be720f:g:IOIAAOSw4A5YrprN

[Nickfromwales]

Ariston are the ones I normally come across / fit, but they are all pretty much the same thing tbh. Heatre Sadia and Redring are known names, along with similar offerings from the better known like Triton. 

 

[Triassic]

Can you clarify if they need a pressure relief valve to be fitted ?

[Nickfromwales]

1 hour ago, Triassic said:

Can you clarify if they need a pressure relief valve to be fitted ?

Page 4

 

Any stored water heater will need expansion and a PRV. If there is a very short run of hot water pipework before the only outlet then you'll also need to fit an expansion vessel, so the PRV doesn't nuisance pass. The manufacturers instructions ( MI's ) will give these particulars to the letter, and they differ with size and make. G3 is required for stored water heaters even under 15L capacity........

 

I thought under 15L got you off the hook for a DIY install but it doesn't seem so. 

 

So basically you'll need a pipe to atmosphere which falls continuously in accordance with D1 and D2 discharge pile work particulars. Again, these will be in the MI's. 

Maybe fit a bigger supply cable and fit an instant?

[Jeremy Harris]

That's interesting, as our boiling water tap has an under-plinth boiler, with a PRV that connects to the sink waste, no expansion vessel and it's supplied as a kit for DIY install, including being pre-wired with a 13A plug.  The MIs make no mention of it needing to be fitted by a G3 competent person, in fact they are written for a DIY type install.  The PRV lets by regularly, every time the unit heats up, and the integrated trap that's part of the PRV waste connection relies on the PRV regularly letting by to keep it topped up.  The PRV in question is also the pressure, and hence flow rate, regulator for the tap, and has a knob on top for pressure/flow adjustment.  This unit can be supplied with a TMV, so that it can also feed a hot tap at a safe temperature, as well as the boiling water outlet.

 

Edited July 15, 2017 by JSHarris

[dpmiller]

does it depend on the volume of the boiler maybe?

[ProDave]

The Hyco one I linked to is all self contained and has no provision to connect any external relief valve or discharge pipework.  I know of one working well feeding a sink immediately above it, and a basin probably 6 metres of pipework away with no issues and nothing fitted external to the unit, just cold water in and hot out to the two taps.

[Ferdinand]

14 minutes ago, ProDave said:

The Hyco one I linked to is all self contained and has no provision to connect any external relief valve or discharge pipework.  I know of one working well feeding a sink immediately above it, and a basin probably 6 metres of pipework away with no issues and nothing fitted external to the unit, just cold water in and hot out to the two taps.

 

Looking at the eBay item you linked, @ProDave, it says "PRV included - must be fitted in every case" in the description. Perhaps it has changed?

 

F

[Jeremy Harris]

I think that refers to  a PRedV, not a PRV, to ensure that the water pressure cannot exceed the 4.2 bar limit of the unit.

Edited July 15, 2017 by JSHarris

[ProDave]

4 minutes ago, JSHarris said:

I think that refers to  a PRedV, not a PRV, to ensure that the water pressure cannot exceed the 6 bar limit of the unit.

Yes it is fed from a pressure reducing valve, but no (over) pressure relief valve.

[Ferdinand]

7 minutes ago, JSHarris said:

I think that refers to  a PRedV, not a PRV, to ensure that the water pressure cannot exceed the 6 bar limit of the unit.

 

Aha.  

 

Clearly I have some plumbing homework to do!

 

The only pressure relief valve I can recall was the one that nearly blew up Three Mile Island because they left it shut.

Edited July 15, 2017 by Ferdinand

[Jeremy Harris]

One problem is that the abbreviation PRV can refer to either a Pressure Relief Valve (one that opens to vent an excessive pressure to a drain) or a Pressure Reducing Valve (one that limits the incoming water pressure to a certain safe value).

 

Here we seem to have adopted the terminology PRV to means a Pressure Relief Valve and PRedV to mean a Pressure Reducing Valve, but that's not very widespread elsewhere.

[Nickfromwales]

7 minutes ago, JSHarris said:

One problem is that the abbreviation PRV can refer to either a Pressure Relief Valve (one that opens to vent an excessive pressure to a drain) or a Pressure Reducing Valve (one that limits the incoming water pressure to a certain safe value).

 

Here we seem to have adopted the terminology PRV to means a Pressure Relief Valve and PRedV to mean a Pressure Reducing Valve, but that's not very widespread elsewhere.

We're pioneers, that's why  

?

[Nickfromwales]

Fyi. 

 

[ToughButterCup]

On 15/07/2017 at 10:51, ProDave said:

Yes it is fed from a pressure reducing valve, but no (over) pressure relief valve.

 

Unit on order.... so now @ProDave, can you nudge me in the right direction for a PReducngV please?

[PeterW]

What is it feeding @AnonymousBosch as I really like these for simplicity. 
 

https://www.bes.co.uk/possi-valve-compression-x-compression-16677

 

Isolator, filter and PRedV all in one. 

[ProDave]

I bought one from Screwfix for the static caravan but it was more expensive than the BES one that Peter linked to above.

[richi]

I used the Stiebel Eltron instant undersink unit:

 

Edited April 11, 2020 by richi
reduce HUGE imge