I am looking to buy a pressurised cylinder for my house and the plumber has recommended either a Megaflo or Santon. Apparently both made by the same company but under different brand names. He usually fits Megaflo's as they are a neater solution (Santon's have an external expansion tank apparently) but in our case, suggested looking at the Santon as ours will be hidden in the garage.
Given the price difference (=A3350), it would seem sensible to go for the Santon however I was wondering if anyone has had any experience or any views on the 2 options. Part of me says that going for the more expensive option would be safer but if they are ultimately of the same quality with the same guarantee......
There is a (rather old) discussion on this very subject over at DIYnot:-
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you thought about a thermal store instead? Theoretically safer, easier to install and no need for the annual service... Or perhaps the Vailant 937 combi with it's built in store.
Though the basic principle of a body of hot water under pressure relying on various mechanical devices to prevent a steam explosion - a remote probability but a devastating consequence - is the same.
I have just spoken with Megaflo technical support and they said that there are 2 main differences...
the Santon has an external expansion vessel
the lady checked with a colleague and said that the Megaflo has pipework which seperates the hot and cold water. When I asked what this meant, she said that the Santon mixes them (i.e. the hot from the tank mixed with the cold inlet). This seems very odd to me and looking at their installation manuals online, the pipework diagrams look identical except for the external expansion vessel.
I have just spoken with Megaflo technical support and they said that there are 2 main differences...
the Santon has an external expansion vessel
the lady checked with a colleague and said that the Megaflo has pipework which seperates the hot and cold water. When I asked what this meant, she said that the Santon mixes them (i.e. the hot from the tank mixed with the cold inlet). This seems very odd to me and looking at their installation manuals online, the pipework diagrams look identical except for the external expansion vessel.
that pressure relief valve had been replaced with a blanking plug.
I think it takes a fair degree of determination & incompetance to blow one up. For many folk, the risk of this happening with a competantly installed cylinder is small enough for them to bear.
I'd image that the number of explosions resulting from an unvented cylinder heated by a conventional boiler must be in the order of zero.
Not so. Stop being silly. Look at the links and what was posted. A T&P valve failed on one which took off through the roof and landed a few streets away. T&P valves are on UK cylinders. In the UK they have to be serviced (£100 per year) and if not the T&P valve can seal up solid over time if not opened or tested and a failure .............boooooooooooom. The text I posted emphases servicing. Will this be done on all of these cylinders? Not course not.
Many of these cylinders are time bombs. There is a near zero-risk superior alternative. Use one of those.
They have the potential for dormant faults that can accumulate over time. When there have been lots about for about thirty years you will hear about more explosions as the safety devices fail. Then there will be a law passed that requires annual inspection to check all the safety device work.
I wasn't really questioning the advisability of having an inspection, I'm just curious as to who has to do this inspection and whether it's actually enshrined in law. Is it actually specified anywhere that it has to be a professional installer who does the inspection or can it be any "competant person"?
It is enshrined in law. Only approved installers can install or service these devices. No DIY whatsoever. You can DIY gas if you are "competent", not unvented cylinders.
To say it is enshrined in law I think overstates it as I do not believe you necessarily commit any criminal offence by installing or servicing an unvented tank yourself.
The relevant extract from the building regulations 2000 section 13 is:
(4) Where building work involves the provision of a hot water storage system in relation to which paragraph G3 of Schedule 1 (hot water storage) imposes a requirement, a building notice shall be accompanied by a statement which specifies -
(a) the name, make, model and type of hot water storage system to be installed;
(b) the name of the body, if any, which has approved or certified that the system is capable of performing in a way which satisfies the requirements of paragraph G3 of Schedule 1;
(c) the name of the body, if any, which has issued any current registered operative identity card to the installer or proposed installer of the system.
So you have to pre-notify and if the BCO does not like what you are doing it will not be approved
The guidance part of the Approved Document G3 then says:
3.8 The unit or package should be installed by a competent person, i.e. one holding a Registered Operative identity card for the installation of unvented domestic hot water storgage systems.
Note *should* not *must*. So again if the BCO is happy with what you have done or for some reason does not realise it was a diy job and signs it off then I cannot see that an offence has been committed.
I stand by to be corrected if someone can point out other bits of legislation.
First the external or internal expansion vessel. You'd think that the internal vessel (essentially an ullage pocket in the cylinder itself) would simplify things. However IME the air pocket keeps dissolving away (in a time scale of months) and requires renewing (by partially draining the cylinder - whihc is easy enough).
If you are an organized and competent owner then there is no problem. IME
99% of owners aren't and the internal pockets all dissolve away and all the cylinders then dribble water out of the the discharge pipes.
Obviously with the external ones the only problem apart from finding somewhere to put it occurs if the vessel fails. On balance the external vessel wins in my book for 99% of ordinary users.
The other matter relates to the the blending of Hot and Cold supplies. The Megaflow does not do this. It has a pressure balanced CW outlet so the supply of H and C is at the same pressure as the cylinder. Thus enabling non thermostatic mixers to function pretty well.
Some cylinders (Santon dunno, Elston certainly) thermostatically blend the outlet HW with CW to produce a consistent and reasonable HW temp. This mainly for cylinders which are heated by electricity (off peak) so they can store water at 75C but blend it to 55C as it is drawn off. With an indirect heating coil the thermostat sets the cylinder temp to (say 57C) and blending the output is not so important.
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