Megaflow v. Combi

[Handyman]

Every combi system I've ever come across never seems able to produce hot water at reasonable flow: Turn the flow up and the temperature drops. Keep the flow down to keep temperature up, and it takes ages to fill a sink, or whatever. Add to this someone running cold water or flushing the bog, and flow rate abruptly changes again, increasing temperature but reducing flow. Indeed, I actually hate combi systems.

Question: Will a Megaflow system give me the same problem, or will high flow rates be maintained at high temperature - even if someone runs cold water from another tap?

 

[oilman]

Megaflo will substantially cure your problem. The problem will be later when the maintenence costs (if it needs things replacing) will surprise you.

 

[chrishutt]

Some of the problems you describe relate to poor cold mains flow, which will also affect the performance of an unvented cylinder. Lots of threads on here describe ways of dealing with this problem.

 

[corgiman]

I must say Oilman, the maintenance and parts replacement is significantly less than a combi

 

[toasty]

I've got a stanton 300l mains pressure (like a megaflow) and there really is no shortage of hot water, as long as your mains flow is good.

Put the plug in while you have a shower and the bath is full in no time!!

The flow really is amazing, I get well in excess of 30litres per minute. The shower is so powerful that I end up backing the pressure/flow off a bit most of the time, the full rate is really not for the feint hearted.

Cheers!
-Dan

 

[ChrisR]

Have both! You could go for a combi with a (small) unvented store which it keeps hot. Alpha CB50 is one of very few condensing ones. ENough stored for a good shower. No backup immersion if it fails, but it IS wall mounted. There are other options.

 

[Paul Barker]

Gravity hot water and a power shower sounds best in your situation?

 

[meldrew's_mate]

I've got a stanton 300l mains pressure (like a megaflow) and there really is no shortage of hot water, as long as your mains flow is good.

That's the secret of a low interactive DHW system, LARGE mains all the way to the cylinder with as few bends as possible.

In addition any (most?) cylinders have an immersion heater as an emergency backup which buys time when (if) the wet heating fails.

 

[Handyman]

Gravity hot water and a power shower sounds best in your situation?

Not when it's impossible to get a header tank higher than 12" above the upstairs shower head. I can put the Megaflow cylinder in the basement right next to the boiler and immediately underneath the kitchen sink: Instant hot water at the sink.

 

[corgiman]

Have both! You could go for a combi with a (small) unvented store which it keeps hot. Alpha CB50 is one of very few condensing ones. ENough stored for a good shower. No backup immersion if it fails, but it IS wall mounted. There are other options.

I agree i have done this a couple of times, best of both worlds

 

[Handyman]

Pah! Why are so many plumbers obsessed with combi boilers?

It's Saturday afternoon and I've just returned from sorting out a combi boiler which had a mind of its own, going off even if timer and thermostat said 'on'. Sorted it out by boosting the pressure to 1 bar, whereas the CORGI plumber who fitted it told the woman it was OK at 0.5 bar, which was below minimum value stated in instruction book, thus causing the boiler to shut off.

Mine's going to be a Megaflow, powered by a nice, efficient - and small - condensing boiler.

 

[corgiman]

we are not "obsessed" with combi boilers you just asked for our opinion.

dont know why you did anyway as with all your sorting out combi's you are obviously registerd with CORGI and appropriately trained

 

[Paul Barker]

Putting cylinder in basement, just be aware you need minimum 30mm drop from tundish before first bend. In most basements this is not achievable whilst trying to remain above a drain.

Not insurmountable, you can either sump and pump it or soak it away, but it adds to your costs.

Pressure at the shower sin't a problem with the power shower I suggested. However you do have a problem with hot water from a gravity circuit if you don't have loft space for sure.

By all means go unvented in preference to combi if you can afford the extra cost. You might be looking for another location that the cellar though.

There are now so many obstacles to legitimate plumbing/heating installations you have to really think it through.

 

[Handyman]

dont know why you did anyway as with all your sorting out combi's you are obviously registerd with CORGI and appropriately trained

No, I'm not CORGI registered. I just followed the customer's instruction manual because the old lady concerned couldn't understand it.

It seems that many people down here have been persuaded to install a combi boiler. My impression (rightly or wrongly) is that it's the easy option for the installer, rather than the best thing for the customer who, in many cases, complains to me that a) their airing cupboard is no longer warm, or b) the boiler is twice as large as they expected, or c) it takes ages to run a hot bath, or d) insufficient flow to satisfy sink and shower simultaneously. (a) and (b) give me work, because they want new cupboards built, or whatever, so I have no problem there. (c) and (d) I experience at both my son's and my daughter's homes.

Please don't get me wrong, as I fully appreciate that combi boilers meet a need and are designed to do a job, but it seems that the local installers here don't necessarily explain the differences when offering them to customers as replacements for storage tank type systems.

As I say, I will go with what my CORGI plumber recommends, and that is a Megaflow system installed in the cellar, with a compact condensing boiler (similar to that which he installed in my previous home about 2 years ago). I leave it up to him to install it correctly.

 

[Paul Barker]

Yes well I have to say that's all cock on. However we don't all deliberately push people towards combis. I give people the information needed to make an intyelligent decision, some people still make stupid ones; I don't impose my will, so in goes a stupid system, I'm here to make a living.

You have chosen an excellent system. I tend to use the oso cylinder because it is cheaper, and larger proportion of it's capacity utilised for water (rest for bubble), same quality, same guarantee. L:ike the megaflow it can be flooded (converted to external expansion vessel) if you need greater capacity in future.

Please spend as much as you possibly can on the boiler, and get a Magnaclean installed.

Keep up the good work helping old ladies, the world today has no consideration for their needs, tv's that won't work without a remote that is far to complexed for them, boilers that need monitoring and repressurising.

There is still a place for open vented systems and gravity hot water. I fit both quite a bit, I vertually give my labour for the extar installation effort because I am so delighted to be doing the right thing for them.

On a personal note I am fortunate to have a tall house so gravity hot water is excellent, airing cupboard is walk in, wife would probably leave me if I put her a combi in.

Of course I should be pleased so many people havce combis, but quite honestly it's repair work with stress, people who have combis get all falseto down the phone, anyone would think the end of the world had come. always leaves me thinking, should have thought of that before you had your airing cupboard wrecked. I mean all houses had them didn't they?