DHW Cylinder Recommendations

[Andy Barron]

I am replacing my boiler in the spring and have decided on WBGreenstar although I haven't chosen the model yet. This is complicated by the fact that we are also looking at building an extension but boiler replacement won't wait this long.

Eventually I would like to make use of solar water heating so it would seem sensible to replace the DHW cylinder with a suitable one at the same time. This is also a good time to change to a pressurised system rather than vented.

The prices seem to range from about =A3600 to =A31700 and some makes I have found are Hetrae Sadia, Santon and Gledhill. Anyone got any advice or recommendations for a suitable cylinder, do you really get what you pay for?

TIA

Andy

[David Hansen]

On Fri, 29 Jan 2010 06:00:36 -0800 (PST) someone who may be Andy Barron wrote this:-

Any particular reasons for doing so?

[Dave Plowman (News)]

I pondered when fitting the new boiler.

1) No possibility of pumping over. 2) Any leak restricted to contents of system 3) Removing the header tank gives me some useful storage space. 4) Not *quite* the same need to balance rads as you can have a higher flow rate without any danger of 1) 5) The boiler fitting instructions seemed to think it mandatory - and it came with a fitted pressure vessel anyway.

[Andy Barron]

To get decent hot water flow to the kitchen and shower, and to get rid of the header tanks mainly. Aren't pressurised systems less likely to corrode on the primary side as well since they aren't 'open' to air?

[Fredxx]

A boiler supporting a sealed system only needs a single 22mm feed from the header tanks with no additional expansion pipe (unless this has changed?)

Fill tank until full, then turn off isolation tap.

Agreed, except it can go virtually anywhere.

Nope. Even with an expansion pipe, it should be able to stop pump over, (or under).

I don't think you can have both - so yes!!

One negative point, is that if I needed to drain, part or otherwise, I could collect the anti-corrosion mixture and put it back into the header tank. It's also easier to add any Fernox or the like with a header tank.

[John Rumm]

One need to take care not to conflate two different things here.

You can have boilers with sealed primary circuits - and these are usually less likely to suffer corrosion for the reasons stated.

You can also have unvented hot water cylinders - these are fed directly from the mains cold supply, and hence operate at or close to mains pressure. These give mains pressure hot water all round the house.

However, you can have a traditional vented hot water cylinder heated by a sealed primary heating system boiler, and you can have an unvented cylinder heated by a vented heating system if you so choose. The two are not co-dependent.

[Dave Plowman (News)]

Yes - but the OP already has an open system. Wanted to know the benefits or otherwise of changing that to a sealed one. On a new install, probably no contest.

[Doctor Drivel]

Eventually I would like to make use of solar water heating so it would seem sensible to replace the DHW cylinder with a suitable one at the same time. This is also a good time to change to a pressurised system rather than vented.

The prices seem to range from about £600 to £1700 and some makes I have found are Hetrae Sadia, Santon and Gledhill. Anyone got any advice or recommendations for a suitable cylinder, do you really get what you pay for?

[Vortex5]

I converted my system to sealed about 5 years ago and have never looked back.

The main benefit has been to reduce flow noise and the ease of filling and bleeding the system after any kind of draining. Plus of course eliminating the header tank...less corrosion etc.

The main noise source was the pump, and it would take days or even weeks after any kind of system refill or top up for the noise to subside. Secondary benefit is the ability to turn up the pump speed a notch to improve flow to a remote radiator.

I have most recently upgraded with a DPS

Xcel 2009 thermal store. This sits in the boiler primary circuit and can be installed as a sealed system, which I have done. This is not a DHW cylinder as such. HW is made in "real time" from mains water via a heat exchanger. As a result all domestic water is now mains pressure. The water header tank is now redundant and a very annoying shower pump has been removed and I am "solar ready". Very happy so far.

[Doctor Drivel]

Yep, the way to go.

[Fredxx]

Not sure why a sealed system should reduce flow noise. With careful siting of the pump, the head of water should add to the pumping pressure.

Automatic filling of a header tank sounds much easier!

I accept this is fast becoming the norm, but the idea of being little independent of the odd interruption of supply does have its attraction!

[David Hansen]

On Sat, 30 Jan 2010 05:36:49 -0000 someone who may be "Vortex5" wrote this:-

That is bad system design/installation, not something inherent in open vented systems.

Why can one not do that in a properly designed/installed open vented system?

The primary water in a thermal store can come from an open vented system. The coil(s) for domestic hot water can be fed from the mains or via a storage tank, whatever one's preference. Thus it is possible to have coils for gravity fed hot water and a mains pressure shower should one wish.

[Andy Barron]

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[Doctor Drivel]

Go for a thermal store/heat bank. Or a high flow quality combi like the W-Bosch 550, ATAG 51kW. Unvented cylinders require an annual service (£60-£00 per ann). A vented heat bank offers so much more - it is also a buffer for the CH. You can have TRVs on all rads an no central wall thermostat as well. No contest.

[Dave]

If the latter, that is very cheap :-)

Dave

[ARWadsworth]

So as cheap as an electric car then.

Adam

[Doctor Drivel]

If you say so. Only an approved man can touch it, install and service. That is £2,000 in 20 years just to store water. Best you do not bother and buy a superior alternative.

[NT]

Once you've stuck the cylinder somewhere, if you make a simple barier round it you can dump waste insulation in there over time, and end up with even less heat loss for nowt. In an airing cupboard, a sheet of thick cardboard across the front does the job.

NT

[John Rumm]

Where does the requirement for annual servicing come from? I often see this mentioned, but no one ever seems to be able to say what legislation triggers the requirement.

[Doctor Drivel]

BS-approved UDHW systems training manual, under the heading of maintenance, p40:

"the installer is responsible for the safe INSTALLATION of the unit. He/she must also make his customer aware that periodic checks of the equipment are ESSENTIAL FOR SAFETY... some manufacturers recommend a MAXIMUM of 12 months. Experience of local water conditions may indicate that MORE FREQUENT inspection is desirable."

BS6700: 1997 states that with unvented cylinders, the "maintenance and periodic easing of temperature relief valves is particularly important".