Undersink waterheater thingummy.

[88v8]

Replacement kitchen mixer to install.
Mains fed.
There's a small undersink water heater.

So, can I just shut off the water and disconnect the pipes to the tap as usual?

The heater has a red canister hanging off it - pressure vessel I presume - with a gauge showing 5 bar. Atop the heater there's a red knob, when I turn it there's a hiss and the pressure drops a bit, then after a few mins it recovers.
Should I depressurise it before starting?

And afterwards do I need to repressurise it - somehow = or does the mains pressure do that for me?
I read the FAQs in the boiler section, is it the same? Don't see anywhere to attach a pump, but I haven't dismantled the cupboard yet.

TIA.

 

[Madrab]

Post a pic of it & stop turning the red knob, that's the safety valve.

 

[88v8]

Oh.
Here it is

 

[JimCrow]

Replacement kitchen mixer to install.
Mains fed.
There's a small undersink water heater.

So, can I just shut off the water and disconnect the pipes to the tap as usual? Yes

The heater has a red canister hanging off it - pressure vessel I presume - with a gauge showing 5 bar. Atop the heater there's a red knob, when I turn it there's a hiss and the pressure drops a bit, then after a few mins it recovers.
Should I depressurise it before starting? No

And afterwards do I need to repressurise it? No
I read the FAQs in the boiler section, is it the same? Don't see anywhere to attach a pump, but I haven't dismantled the cupboard yet.

TIA.

You only need to isolate the cold water supply.

Also that's the wrong expansion vessel you have there, you need a white or blue one for potable water.

 

[dilalio]

That certainly looks to be an incorrect EV!
Get it checked and changed.

I saw over a million quids worth of damage caused by a wrong EV on an under counter water heater in a gents bathroom in a posh London office block... I was first on scene, to a call out for a leak... Ceilings falling down, including air con units... The whole shebang

 

[88v8]

Aha. Another thing I didn't know I didn't know. Not that we ever drink the water from the hot tap.

Anyway, like this?
https://www.advancedwater.co.uk/prod-140-147-0021.html

So, in addition to shutting off the water, should I let the pressure out of the EV first?

 

[JimCrow]

Aha. Another thing I didn't know I didn't know. Not that we ever drink the water from the hot tap.

Anyway, like this?
https://www.advancedwater.co.uk/prod-140-147-0021.html

So, in addition to shutting off the water, should I let the pressure out of the EV first?

No

 

[dilalio]

Not that we ever drink the water from the hot tap.

Nevertheless it is "potable water" and contains all of the minerals and chemicals that are both naturally present, and those introduced by the water supplier. Add continuous heating and cooling, under pressure, into the mix and you have all the components that will eventually lead to corrosion and catastrophic failure of a non-potable water EV.
Just like a burst internal mains pipe, it will cause a lot of damage... Especially if it happens whilst you are away!

 

[88v8]

Today I bought an EV from a local plumbers' merchants.
Doubtless the instructions in the original German were excellent, but the translation is somewhat opaque.

I have tried to look up the procedure for adjusting the pressure and how to determine whether it needs adjusting, but no joy.

The EV is pre-charged at 4 bar. With the water off and drained, the current EV has just under 2 bar, and with the water on the pressure is 5 bar.
So, is 4 bar OK, if not what pressure should I set, and with the water on or off?

 

[88v8]

There's a hole in my bucket... the trouble being that all our buckets get used for gardening and seem to develop holes, even the one I have under the drain valve which is leaking.

Actually that's not true, it's not the drain valve, it's the quarter turn valve ahead of the drain valve. Having shut it off for perhaps the first time in ten years, now the gland is leaking.
So one way and another I need to get on.

This ahh, interesting, thread https://www.diynot.com/diy/threads/...ng-noise-after-h-w-is-drawn-off.319199/page-2 included the advice to set the EV a little below the pressure of the incoming.
As I mentioned, with the mains off I have 2 bar, and with the water on, 5 bar, so that means the mains is showing about 3 bar / 50psi, and on that basis if I reduce the EV to around 2.5 bar, I should be OK ?

Be nice if shops sold stuff made in England, like wot they useter.

 

[polesapart]

[QUOTE="
As I mentioned, with the mains off I have 2 bar, and with the water on, 5 bar, so that means the mains is showing about 3 bar / 50psi, and on that basis if I reduce the EV to around 2.5 bar, I should be OK ?"

No.

Leave the precharge at 4 bar.



"Be nice if shops sold stuff made in England, like wot they useter."

Like mobile phones? Globalisation, dear boy, globilisation. Johnny Foreigner isn't as dumb as we used to think.

 

[88v8]

Just to finish off... not only was the quarter-turn valve leaking, but also the pressure gauge itself started leaking, which at last prompted me to move this from the To Do list to the Do It Blooming Now list.

This happened after the Water Co was mucking around with the pressure while commissioning a new main. The gauge leaked through the face.
So, new 150psi gauge, new blue vessel, set the pressure to 70psi/4.5bar.

Nice to know that we won't be blown up.
Thankyou all.