Unvented Cylinder Vs Tradiotnal Vented - Did I Do This All Wrong?

[Rodders53]

When did your water supply last fail - I live in London and never happened to me

Lucky you. I've lived in Metropolitan Line land and, being at the top of a hill had virtually no water flow regularly (in the summer evenings particularly with people watering their plants).

Here in semi rural Bedfordshire I got £50 credit from Anglian Water for the regular(ish) mains pipe bursts in the village, just last year.

That said I like my Oso unvented HW cylinder with an air bubble in it.

 

[Harry Bloomfield]

When did your water supply last fail - I live in London and never happened to me

More often than we have had power cuts here.

Can you imagine of 200 litres of cold water came through your ceiling with a vented setup? Who says unvented is more dangerous ?

The (tank) water from a vented leak is cold, from an unvented it is hot enough to do serious harm - hence the requirement for inspections and extra qualifications.

 

[Harry Bloomfield]

Noises are a great diagnostic aid,

Talking of which, I have just been in the kitchen and heard a strange to me noise - like a distant, continuous rattle, and I just couldn't track the source down. I went outside, all quiet there, back inside, put my ear to the fridge freezer, that was running, but no sympathetic vibration noises from it. Opened kitchen window to listen again to outside noises and it got slightly louder, tried the boiler cupboard next to the window - nope. Then I looked at the analogue clock, just above the window to check the time, and it was wizzing round at high speed. It's a MSF radio clock, obviously it had just resynched itself and was adjusting - one she brought with her

 

[Madrab]

An unvented system has to share what ever the water mains flow rate is, between the two outlets.

Which is why the mains for an unvented system should be properly surveyed and why there is a recommended dynamic minimum that the mains pressure and flow should be at to minimise any drop off. When I open the CW outlet on my basin there is a peak flow out of the spout, when the HW outlet is then opened there is a significant increases in flow. I'm am lucky though as I have 3 bar dynamic @ 22L/Min

Who says unvented is more dangerous

Unvented isn't more dangerous per sé but if all the safety features did fail and pressure rose enough then it will quite happily take the ceiling/roof off your house hence why it's really important to service the cylinders and their safety controls at the same time as the boiler. If the vent blocked on a vented system then pressure would also build up in the cylinder but the copper would probably fail at a lower pressure and therefore a lot less drastically.

 

[gas112]

all this just fit an unvented nonsense from the diyers an unvented is not a miracle cylinder that will give you super pressure at the outlets throughout the house . You have to have an suitable incoming cold supply in the first place which many properties dont have

 

[bernardgreen]

If the vent blocked on a vented system then pressure would also build up in the cylinder

The maximum cold pressure in a vented system would be set by the head of water in the cold water storage tank ( fixed height )

The maximum cold pressure in a un-vented system is determined by a couple of valves :-
1/ a PRV ( Pressure Regulating Valve ) controlling the pressure in the system
2/ a PRV ( Pressure Relief Valve ) that releases pressure in the system if the PRV (1/ ) fails to regulate the pressure.

My experience ( from industrial control systems ) is that a valve is far more likely to fail than a vent pipe becoming blocked.

Even if the vent pipe did become blocked then there is also the cold feed pipe that would also have to be blocked before the pressure in the hot cylinder could become higher than the maximum cold pressure. ( a reason why a combined vent and feed pipe should be avoided )

 

[Johntheo5]

I have a vented system but I also have a 2bar PRV on the oil fired boiler.

Re unvented cylinder testing, (see below) does this imply that you just lift the valve seat by means of turning the lifting knob on the top or are they meant to be pressure tested to ensure that they lift at their design pressure, is the operating temperature of the T&PRV ever tested. I wonder how many G3s actually do any of this?.
I had decades of marine & industrial experience of high and low pressure steam boilers and the safety valves on these had to be tested (lifted) every 12 to 16 months under operating conditions with a insurance inspector in attendance. Unvented HW cylinders are generally full of water (apart from the air bubble type) so the consequences of a cylinder failure is much reduced as water is by and large incompressible so no expansion effect to blow anything very far, unlike very high temperature hot water which can happen with electric heated HW cylinders, if such a cylinder ruptured at say even 5bar and the HW temperature had reached 160C due to a faulty stat then over 10% of the water will flash off into steam at atmospheric pressure and the expansion effect in falling from 5bar to 0 bar will certainly have a catastrophic effect. Thats why you see Utube videos of rupturing HW cylinders heading for Mars .

 

[gas112]

TPRV are anything up to about 100 quid and the trouble them is they do not always reseat so its a case of that valve that was ok before i touched it now needs changed

 

[vulcancontinental]

Vented:
Simplicity
Gravity
I had 30" from tank base to rose pressure flow no problem, no pump.
Insulate and move gate valves once a year leaving them fully opened then turned back a rotation.
Cost both initial and ongoing is cheaper.

Unvented:
Cost, both initial, ongoing with increased water and energy usage.
Faster flow rate if incoming pressure is adequate.
Expensive components, extra components.
Greater performance potential but you'll pay more for it and be no cleaner or have more hot water but will use more.

It's your money

 

[stem]

If you want to DIY there's only one choice. And this is a DIY forum after all.

Vented:
Repairs can be done cheaply done DIY

Unvented:
All repairs to the cylinder / associated pipework / expansion vessel / Pressure relief valves / controls (thermostat & motorised valve) plus the annual service must be carried out by someone that holds an Unvented G3 (Building Regulations) Certificate.

 

[Millwright]

I have had an unvented for 11 years, would 100% have one again if I moved and the new house didn't have one.

 

[opps]

When did your water supply last fail - I live in London and never happened to me

Ealing, west London, no water for a few hours about 2-3 years ago. I got to work, and left. Twice in a two week period. That said, yeah, seldom happens.

Power cuts are probably more frequent.

 

[OvertonPlumber]

Worth watching what happens when you cap of the safety devices

 

[Millwright]

Worth watching what happens when you cap of the safety devices

There's more than just the safety devices being capped there.....wouldn't happen in a domestic setting, as you'd have to bypass all cylinder safety and also have a boiler which heats water past boiling point, which they don't.

 

[Bod ...]

I avoided installing pumps if there is an opportunity to fit an unvented


However if the pump and tanks are fitted correctly and with some thought fir the customers needs then the system should work well with minimum noise.