Unvented Cylinder - Megaflow or Santon Premier Plus?

[Bcp]

Which unvented indirect hot water cylinder is best do people think - the Megaflow (built in expansion) or Santon Premier Plus (which has the expansion vessel separate)?
Size: 145-150 litres, for a 2-3 bed house with bath & shower.
I'd be grateful for your views, thanks.

 

[Slugbabydotcom]

Megaflow has 25 yr guarantee and is a lot neater. Premier plus is only 10 years guarantee with 5 yrs on the pressure vessel.
pressure vessel wont ever go on the megaflow because there isn't one.

Its horses n courses. I have just got a job to fit premier plus's [pp150e] in 14 flats. I would rather be fitting megaflows but at a saving of £2800+ the man with the money wants the cheaper option.

May I suggest that if you plan on staying in the same house for more than say 8 years that you invest in the Megaflow.

Are you aware that fitting one of these is not a DIY job and failure to report it's installation to the local authority is an offence? see 3.8 on page 11-12 here

 

[Bcp]

Thanks for this. Firstly, let me put your mind at rest - I'm not doing this myself! I have a plumber to do it, but just want to understand some of the issues myself before deciding which cylinder to go for.

The guarantee situation sounds pretty convincing, but I've been told by a Heating & Plumbing shop that the Megaflow has to be (or should be) drained down every six months and refilled, otherwise the air bubble goes and then water drips out of the safety valve. Also you get less hot water from the Megaflow because of the air bubble.

 

[Slugbabydotcom]

I've been told by a Heating & Plumbing shop that the Megaflow has to be (or should be) drained down every six months and refilled, otherwise the air bubble goes and then water drips out of the safety valve. Also you get less hot water from the Megaflow because of the air bubble.

If water runs out of the safety valve it is possible that the air bubble is lost but highly unlikely and theres more chance of the pressure vessel going on a premier plus than that happening.You have to have an air buffer somewhere in the system whether its part of the cylinder or in a vessel. Much neater to have it built in I say.

I would say that the capacity given for the megaflow allows for the expansion space and will vary slightly depending on the water pressure

Go to the heatrae and santon sites to download the installation instructions and specifications for both cylinders and you will see that you have either been mis-informed or perhaps mis-understood what they were saying.

 

[Bcp]

OK, I'll have to think about it all, thanks a lot for your help.
Bcp.

 

[ChrisR]

The reason the air gap in the Megaflo (and othrs like OSO) "needs recharging" periodically is that there is no rubber diaphragm to stop the gas being dissolved. A separate PV, DOES have one so you will not get the same situation, for perhaps several years (like in a combi).

 

[Paul Barker]

Oso is just as well made as mega costs less, gives you more useable hot water as a proportion of the total capacity, is equally covered by a 25 year guarantee, and when your installer has a technical question they are straight there on the end of the phone.

 

[Agile]

In spite of whats said above, the air bubble on most installations does need recharging every 6-9 months. It only takes about 15 minutes but householders see it as a chore and get annoyed! Its essentially to warn them before choosing that model.

Another option is to use the Megaflow AND to fit a separate expansion vessel as well. Its a pity they dont realise just how much problem that internal air gap causes professional installers.

Make sure your installer holds the unvented qualification before he starts!

Tony Glazier

 

[Slugbabydotcom]

In spite of whats said above, the air bubble on most installations does need recharging every 6-9 months.

Tony Glazier

I will bow to the other posters experience on this.... just that the few I have fitted or encountered havent had this problem YET !!!

 

[Agile]

There was an internet posting a few years ago from an unfortunate plumber who had fitted a Megaflow in a loft. He forgot it would need regular bubble reforming and never told the householder.

The householder was a bolshy type who accused him of fitting a substandard product in an unsuitable location!

Tony Glazier

 

[gazthepottertonengineer]

Megaflo's all the way for me

 

[chrishutt]

OSOs, which also have the internal air bubble, can also be modified to take external expansion vessel.

 

[Paul Barker]

Yes like the megaflow the oso can be flooded.

Reform it on your anual visit to service their boiler.

 

[ChrisR]

You can get Pressure Reducing Valves set higher for the Oso - handy if you have 5 bar mains.

 

[Plumbing novice]

I am currently going through a similar experience of trying to choose an unvented pressure system. The Megaflo has the 25yr guarantee, better flow rates and better revoery time than the Santon. However, the Santon has an operating pressure of 3.5 bar vs 3bar for the Megaflo which is making me think Santon is the one to go for. Does anyone know if there is much of a noticable difference between 3.5 and 3 bar for showers.
Thankyou