unvented water cyclinder discharge

[toadhall]

thanks onetap.

I have gone full circle and am now back to a combi boiler. Like 12m londoners, i am resigned to the fact that power showers are for bankers only.

At least it has with no explosive or sludge bucket cylinder in the basement and no sceptic tank in the loft.

 

[toadhall]

Hi onetap
quick question.


My old (middle of the road) combi in my previous house gave a decent shower to the first floor, but if my wife filled a kettle in the kitchen, that was the end of the shower.

As we have only moved to a nearby street, the pressure/flow from thames water is the same so I am reconsidering the combi option.

If i go for a top of the range combi, will my shower pressure die if someone turns on a tap elsewhere in the house? Can decent combi's handle two showers? thanks.

 

[Onetap]

If i go for a top of the range combi, will my shower pressure die if someone turns on a tap elsewhere in the house? Can decent combi's handle two showers? thanks.

Yes, within reason, but then that depends on the flow rate you expect from a 'decent' shower. Just find out the flow rates of hot (mixed) water. You need adequate water and gas flow rates to achieve that, which may involve replacing the service pipes connecting to the street mains. I don't fit boilers, someone may suggest a few contenders.

As we have only moved to a nearby street, the pressure/flow from thames water is the same so I am reconsidering the combi option.

That may be a false assumption, if you don't know the pressure available in the street main or the state of the service pipe. Thames Water have been turning down pressures to reduce leaks; in effect, you'd be using their pump instead of installing your own. Any competent installer would measure the static pressure and the flow rate before quoting for a mains fed system, combi or unvented.

 

[Onetap]

See the details here of 'Converting a standard boiler into a combi-boiler', similar to the Youtube link posted above.

http://www.heatweb.com/techtips/hx/ta.html

This may be worth considering if your existing boiler is newish and you have room in the basement for the equipment.

You should have a PRV (pressure relief/safety valve) on this system, downstream of a pressure reducing valve, neither of these are shown. Nor is the TMV required on the hot water outlet. I'd still want a water shut-off &/or leak alarm on such a thing in a basement.

The dangers of an unvented cylinder bursting explosively are greatly exaggerated; it has never yet happened in the UK. Myth Busters had to do some serious sabotage to get theirs to burst.

Explosive bursts are rare in the US, where there are millions of the things in use, all with only one pressure relief valve instead of the two required in the UK. There have been a few vented cylinders in the UK that have burst after freezing or having been incorrectly installed.

Similarly, cold water storage tanks will stay clean if properly installed and insulated. I've cleaned mine out every few years and have only ever found traces of limescale in it. I used to see some real horror story tanks in lofts when I first got involved in plumbing, a long time ago.

 

[mickyg]

regards sludge in thermal stores, that was why i made the comment regards the heating having its own coil, this stops sludge build up as the boiler, heating circuit and store are all indivdual to each other.
They can however suffer with limescale issues and I would recommend having a softener.
Also to comment on the plate heat exchanger setup in the video, I would be very cautious with this kind of installation unless the boiler is a decent power which is unlikely for a heat only in a small terrace.
A 15kw boiler with heat losses is only going to give you the same performance as a decent electric shower. Not sure either why they used 2 plate he's when one of the correct or slightly oversized would have been adequate, and also I'd be concerned about the amount of water wasted waiting for it to heat up...but hey its one idea !

 

[mickyg]

The dangers of an unvented cylinder bursting explosively are greatly exaggerated; it has never yet happened in the UK..

you mean it has never yet happened to one that was correctly installed

http://www.wareonline.co.uk/news/article.asp?id=153

 

[toadhall]

thanks for the advice guys. My problem is compounded by having a rubbish boiler that was going to be replaced in stage two of my grand design. If the combi can work, i think it may be the esiest option.

The plumber has measured my pressure while I was at work and I have 17Litres per minute flow and 3bar standing pressure.

The high end combi's have a flow rate of 17litres per second.

Does this mean this combi will power two showers at 8.5litres per second?

Is that any good? Sounds ok to me..........

 

[Dan Robinson]

No it will be rubbish and vastly over powered for your house/flat.