Electric shower vs. instant water heater

[Triassic]

I had a look at the product on line this morning and there is no mention of the need to install these additional items. Makes you wonder how many people buy the heater and never realise the need for the expansion vessel or releif valves.

[ProDave]

17 minutes ago, JSHarris said:

 

Curious.............

 

We have a boiling water tap with a heated reservoir under the plinth, and that has to have a PRV and tundish, in fact it's supplied with one.  The PRV is of the type that can operate regularly, every time the tank heats up and the water expands, as it needs to in order to keep water in the trap under the tundish (all part of the same moulding).  Similarly, when we had these under-unit hot water heater at a place I worked, they had a separate tap and outlet, and the outlet was the expansion opening, as it was connected to the tank, the tap just turned on cold water to displace hot water and drive it out the outlet.  The over-sink units are the same, I believe.  I also remember an over-sink very hot water dispenser (for making tea and coffee etc) that had an overflow pipe led into the sink, that I always assumed was connected to a PRV.

 

Be interesting to find out how the 20 litre unit mentioned deals with expansion and pressure relief.

I changed a Hyco under sink electric water heater recently. that didn't have an expansion vessel nor a visible tundish.

 

Likewise I wired a Quuker boiling water tap, one that sat upright under the sink unit, and again I saw no tundish.

 

So if your had a prv and tindish, where did you drain it to?
 

[Triassic]

I sent my requirements to Stirbel Eltron and they recommend the DHC-E 8/10. This will be used to supply a kitchen and bathroom sink. Can anyone suggest an online supplier?

[Jeremy Harris]

7 minutes ago, ProDave said:

I changed a Hyco under sink electric water heater recently. that didn't have an expansion vessel nor a visible tundish.

 

Likewise I wired a Quuker boiling water tap, one that sat upright under the sink unit, and again I saw no tundish.

 

So if your had a prv and tindish, where did you drain it to?
 

 

 

Our Itho boiling water tap came complete with the tundish and trap, plus an adapter to fit it to a 1 1/2" waste pipe.  There are details on this blog entry, towards the bottom, with a photo of the installation inside the cupboard under the sink: http://www.mayfly.eu/2014/04/part-twenty-nine-some-details-that-may-be-of-interest/

 

Here's the photo from there that shows the PRV and tundish:

 

 

The PRV is right next to a needle valve flow rate adjuster, hidden partly behind the grey waste pipe in the centre.  The tundish, with integral water trap, is the black thing in the centre.  What looks like a normal compression tee is actually a special, that allows the waste pipe to go right through it.  The MI's say to cut a vee into the top of the waste pipe, then slide the tee fitting on so that the vertical bit is over the cut out, then fit the tundish reducer/adapter to the top.

 

Cold water feeds into the flow rate adjustment valve from the 15mm copper on the left, and the cold water feed to the under-plinth tank is the flexible pipe to the right of that.  This pipe also acts as the pressure relief pipe, as the PRV is in the top centre of the tundish.

[ProDave]

The reason I asked is I thought discharging (potentially) boiling water into PVC waste pipe was not allowed?

 

There is an nhbc document around that details how you can use a waterless hepco trap and a particular type of plastic pipe (not pvc, I forget which) to discharge into a stack, but it must be a direct run to the stack in that particular type of pipe that can withstand boiling water.

 

I am currently thinking about the plumbing for our UVC and to be honest the run to do that would be far too long, so I am now looking at dropping a copper pipe down inside the internal walls and out through the blockwork under the ground floor level.
 

[Jeremy Harris]

2 minutes ago, ProDave said:

The reason I asked is I thought discharging (potentially) boiling water into PVC waste pipe was not allowed?

 

There is an nhbc document around that details how you can use a waterless hepco trap and a particular type of plastic pipe (not pvc, I forget which) to discharge into a stack, but it must be a direct run to the stack in that particular type of pipe that can withstand boiling water.

 

I am currently thinking about the plumbing for our UVC and to be honest the run to do that would be far too long, so I am now looking at dropping a copper pipe down inside the internal walls and out through the blockwork under the ground floor level.
 

 

I'm guessing that they get around that by discharging via the cold feed, so the tiny drips of expansion water that comes out of the PRV will usually not be boiling, but just a bit warm.

 

In the event of a fault, then it's no different to me running the boiling water tap into the sink above, is it?  I do that all the time, to run off the bit of less than boiling water before making a cup of tea, and to rinse out the small re-usable milk bottle I take over to the new house to disinfect it.

[Nickfromwales]

2 hours ago, ProDave said:

I am currently thinking about the plumbing for our UVC and to be honest the run to do that would be far too long, so I am now looking at dropping a copper pipe down inside the internal walls and out through the blockwork under the ground floor level.

I always run these in copper TBH. It's not the type of pipe you want letting you down. 

Read the G3 docs as for a D2 run over 3m you need 28mm and a max run of 12m total iirc. Bends are 1/2m again iirc.

You need D1 to drop at least 400mm vertically to the tundish and D2 needs to drop at least 400mm vertically after the tundish before any invert, but the more the better TBH. Go 28mm as soon as possible.

whats the length of the run?

[Nickfromwales]

4 hours ago, Triassic said:

I had a look at the product on line this morning and there is no mention of the need to install these additional items. Makes you wonder how many people buy the heater and never realise the need for the expansion vessel or releif valves.

Some small units rely on the DHW pipework for the expansion. 

Itll be in the installation manuals, but if rebranded Chinese crap from b & q then its Russian roulette. 

[Crofter]

Seeing as this is no longer about electric showers or instant water heaters, I've started a new thread on UVCs...

 

 

[Nickfromwales]

??

@ProDave, copy your last over to there and we'll carry on accordingly ?

@ me so I get a ping .