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Combi v Megaflow

(14 Posts)
Chris3630 Sun 05-Jul-15 11:13:45


Seeking clarification on best solution - am getting different opinions in various quotes:

Summary of my house:
- Creating 9m x 6m ground floor extension requiring wet underfloor heating
- New loft bathroom with shower
- Existing family bathroom with bath/shower
- Usual washing machine/dishwasher
- Upgrading the Thames Water Mains pipe to the thicker blue pipe
- Shower product to have 22mm/largest pipe available for water delivery

2 adults and one teenager in the house. Very rare to require a bath and shower at the same time.
Will have underfloor heating at morning and evening shower/bath times

Would like a good strong/pressure shower at all times.

Options are:
1. Boiler & megaflow type solution
2. Worcester Greenstar 550CDI Gas Combination Boiler

Please can you advise on best option to fulfill the above.


lalalonglegs Sun 05-Jul-15 12:47:39

Megaflo every time - even if you don't have baths/showers simultaneously, I have always found that showers tend to run cold in homes with combi boilers if someone runs the kitchen tap/washing machine/brushes teeth in the other bathroom. Very irritating indeed.

PigletJohn Sun 05-Jul-15 13:30:45


if you have not laid the new pipe yet, ask for 32mm. The cost is not much more than 25mm.

Insist on full-bore stopcocks and service valves, all the way into the house and boiler, and on your internal pipes to bath and shower, hot and cold. Sorry the bigger ones do cost a bit more (which is why they are often omitted). Smaller ones will strangle the flow.

Chris3630 Sun 05-Jul-15 13:38:30

Thank you

Chris3630 Sun 05-Jul-15 18:27:35

Thanks - the 32mm piping you refer to - is that from boiler/megaflow connecting to radiators. showers. baths & taps?

kali43 Sun 05-Jul-15 19:13:36

maxing out on boiler lurking so marking this for later!

PigletJohn Sun 05-Jul-15 20:14:56

32mm is the blue polypipe, preferably running all the way from the mains in the pavement to the stopcock under your sink. It is measured on outside diameter, and has thick plastic walls. If you take a 22mm copper pipe off that to each bathroom, you will have plenty of flow. You cannot run a bath in a reasonable time using 15mm pipes.

The Megaflo probably has a 22mm copper pipe going in and coming out of it, I recommend teeing off from this a 22mm to each of your bathroom(s). If it has a 28mm connection, use that and tee off the bathroom pipes from it. That will enable you to run two baths at the same time with good flow.

The kitchen sink only needs a 15mm copper pipe for both hot and cold, and the smaller size will not take so long to run hot.

Unless you have an unusually big house, 22mm and 15mm copper will be plenty for each floor of your radiators.

I know some will say I am over-generous in my sizings, but I'm not concerned about saving a few pounds, and the annoyance caused by undersized pipes throttling the flow is out of all proportion to the tiny effort of running big pipes in the first place. It is a lot of work and expense to try to improve it later. I bet you are spending thousands on your new boiler, cylinder, bathroom and showers. The pipe costs are much smaller.

I think you will be astonished and delighted by the flow you get, the speed of filling your bath, and the power of your shower. If you decide to reduce the flow a bit later, that's easily done.

whiteagle Sun 05-Jul-15 20:21:57

I'm in the same situation and decided on the invented cylinder and system boiler option. Been doing lots of research and going for an OSO cylinder - much cheaper than megaflo which is, after all,.just a brand of invented cylinder.

lolalotta Wed 23-May-18 09:48:03


spydie Thu 24-May-18 19:44:08

Pretty much identical situation with regards extension and heating/number of showers... but extended last year. We had a megaflow/boiler combination that was just useless. 1 bath or shower and that was it, hot water gone. We had the Worcester greenstar installed at time of extension, along with additional bathroom and downstairs underfloor heating. It's fabulous. We have had guests using both showers at the same time with NO heat or pressure issues, even whilst the heating is on and washing machine or dishwasher on the go. Honestly one of the best choices we ever made. We also freed up a tonne of space losing the megaflow too grin

yomellamoHelly Thu 24-May-18 20:42:12

Just gone from Megaflo to massive combo. Water pressure is definitely less than previously. Do like the fact that we have hot water on demand but not sure it outweighs the water pressure.

johnd2 Fri 25-May-18 10:02:17

We had a small restrictor widget in the boiler water inlet that was restricting the flow, took that out and things improved a lot.
I think the widget is only there to guarantee the boiler can make the maximum target temperature even in winter, but who has a shower at 65c anyway?

Tinkobell Fri 25-May-18 18:36:26

No question of it. If you've got the space, Megaflow.

RubberTeeth Fri 25-May-18 19:34:44

What if you're on the top of a hill? Love Megaflow idea and upgrades as suggested, but been told I need an accumulator or break tank to address pressure and flow issues. Is this expensive bollocks?

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