Megaflow + Combi-boiler? (installation costs fair?)

1 Jul 2004
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London (North)
United Kingdom

I currently have a Potterton 28i Combi Boiler. It has had a problem with the hot water supply, that has been put down to (hopefully) heat exchanger.

The cost of repair is said to be Parts - £90. labour £50.

However, we've never been able to have two showers running at the same time, and always had a problem with the hot water. Apparently this is due to the size of the house (it's very long bungalow, 3 bed, 2 bath, kitchen, utility, two large reception rooms).

So the suggested plan is this.

1. Use the Combi-boiler just to run the central heating.

2. Use a megaflow (or similar) 210l tank to run the water for two bathrooms (inc showers simultaneoeously), kitchen, and utility.

I want a system where if a toilet is flushed someone won;t almost die in the shower! And that two showers can occur without problem.

The total cost, parts of repairing the combi, the cost of the megaflow, installing it and a drain/clean of the whole system


is that fair?

is this a good idea?

Any other suggestions?

All mush appreciated.

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Updated, now I know a bit more what I'm talking about!

Oh can Megaflow's be used with electric showers, or is the pressue too great?
Updated, now I know a bit more what I'm talking about!

Oh can Megaflow's be used with electric showers, or is the pressue too great?

An electric shower connects to your mains cold supply and heats the water, so no - you won't be able to use an electric shower with a Megaflow.

As the water from a Megaflow will be heated and pressurised, you'll need a thermostatic shower mixer, which will mix the supply from the Megaflow with the cold mains supply.
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What about the cost of the installation, and is using a megaflow a good idea?

Sorry - I'm a DIYer, so can't comment on the installation cost.

Using a Megaflow is certainly one solution to the issue of a household with high hot water demands and should enable you to run two showers at once.

Just make sure you're clear in your own mind about the types of shower that are suitable to use (ie. not an electric or 'power' shower if you currently have either of those) and as far as I'm aware, you'll need a 22mm mains cold water connection to it.

A more powerful combi (eg 37 or 42kW) may also be able to provide hot water to more than two outlets at once, although you'll need a decent mains pressure/flow and a gas supply to match the highest demands of the boiler.
Blind leading the blind!

Any of those mentioned solutions will need a very good mains supply to the property and measuring that is the first priority.

It can usually be upgraded for about £1000 +

For one shower you need a minimum of 15 li/min for two a minimum of 25 li/min but those are minimum flow rates

You need to take the advice of a competent CORGI/G3 registered installer!

this is the solution of a registered Corgi installer. not sure about the G3 bit!

I assume that he looked at all of that before suggesting.
Blind leading the blind!

Well that put me in my place, didn't it ? If you were able to point out any mistakes in my posts, then I think the OP would find that far more useful and I would learn in the process - wouldn't that be slightly more constructive ? :rolleyes:
There was nothing wrong with anything you said, Mike!

BUT, before anyone considers any mains powered solution the first thing is to measure the dynamic flow rate! Thats the litres per minute while say 1 Bar residual pressure remains! The open pipe flow rate will give an idea but is not definitive.

If the OP's "plumber" did not measure the flow rate then he was not acting very professionally.

The G3 relates to the building regulation for which a qualification has to be held to install unvented cylinders ( or boilers containing them).

well we do currently have a mains powered system - being a combi-boiler.

However, i do understand that we must check whether the rate of flow is enough.
You haven't said whether it will be a direct cylinder heated by electric immersion or if it will be an indirect unit heated by the combi with the control gear needed this would have a large bearing on the price. Did the chap that suggested this physically measure the water flow at an outlet? Big difference between your current setup giving 11 litres a minute and an unvented giving potentially 35 litres.
I'm just removing an 18 month old Megaflow 210, the perfomance is fantastic and the heated water is good for a couple of days if you dont have the immersion on every night (obviously dependent on usage).

It cost me £1,100 installed including removal of old tank and I'm only removing it to have a combi fitted because I had enough of my stupid Economy 7 storage heaters. (it's on EBAY if you're interested lol but as other posts have said, need G3 installer).

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